Piezoelectric device having a ferroelectric film including a ferroelectric material

ABSTRACT

A method of manufacturing a ceramic includes forming a film which includes a complex oxide material having an oxygen octahedral structure and a paraelectric material having a catalytic effect for the complex oxide material in a mixed state, and performing a heat treatment to the film, wherein the paraelectric material is one of a layered catalytic substance which includes Si in the constituent elements and a layered catalytic substance which includes Si and Ge in the constituent elements. The heat treatment includes sintering and post-annealing. At least the post-annealing is performed in a pressurized atmosphere including at least one of oxygen and ozone. A ceramic is a complex oxide having an oxygen octahedral structure, and has Si and Ge in the oxygen octahedral structure.

This is a Continuation of application Ser. No. 11/987,971 filed Dec. 6,2007, which in turn is a Continuation of application Ser. No. 11/314,996filed Dec. 23, 2005, which in turn is a Continuation of application Ser.No. 10/166,707 filed Jun. 12, 2002. The disclosures of the priorapplications are hereby incorporated by reference herein in theirentirety.

BACKGROUND

The present invention relates to a ceramic and a method of manufacturingthe same, a dielectric capacitor, a semiconductor device, and otherelements including the ceramic of the present invention.

As a ferroelectric film applied to semiconductor devices (ferroelectricmemory (FeRAM), for example), a ferroelectric film having a perovskitestructure (PbZrTiO-type ferroelectric film, for example) and aferroelectric film having a layered perovskite structure (BiLaTiO-type,BiTiO-type, or SrBiTaO-type ferroelectric film, for example) have beenproposed. The ferroelectric film having a layered perovskite structureis generally formed by crystal growth from an amorphous state.

In the case of forming a ferroelectric film having a layered perovskitestructure by using this formation method, the crystal growth rate in thec-axis direction becomes lower than those in the a-axis direction andthe b-axis direction due to the crystal structure of the ferroelectricfilm. Specifically, crystals tend to be grown in the a-axis directionand the b-axis direction. Therefore, a ferroelectric film having alayered perovskite structure formed by using the above method has arough surface morphology, whereby openings (holes or grooves, forexample) are easily formed between crystals of the resultingferroelectric film. Generally, the above-described ferroelectric filmmust be sintered at a temperature as high as about 600 to 800° C. for along period of time. Therefore, when forming a ferroelectric memory bycombining a ferroelectric capacitor using such a ferroelectric film witha semiconductor element, it is necessary to prevent the semiconductorelement from being affected by the high temperature treatment for a longperiod of time for forming the ferroelectric film. This gives rise toproblems such as complexity of the manufacturing process for theferroelectric memory.

SUMMARY

The present invention may provide a method of manufacturing a ceramiccapable of lowering the crystallization temperature of the ceramic andimproving the surface morphology of the ceramic.

The present invention may also provide a novel ceramic obtained by themethod of manufacturing a ceramic of the present invention.

The present invention may further provide a semiconductor device andother elements to which the ceramic of the present invention is applied.

A ceramic according to one aspect of the present invention is a complexoxide having an oxygen octahedral structure, and comprises Si and Ge inthe oxygen octahedral structure.

A method of manufacturing a ceramic according to another aspect of thepresent invention comprises forming a film which includes a complexoxide material having an oxygen octahedral structure and a paraelectricmaterial having a catalytic effect for the complex oxide material in amixed state, and performing a heat treatment to the film, wherein theparaelectric material is one of a layered catalytic substance whichincludes Si in the constituent elements and a layered catalyticsubstance which includes Si and Ge in the constituent elements. The heattreatment may include sintering and post-annealing, wherein at least thepost-annealing may be performed in a pressurized atmosphere including atleast one of oxygen and ozone. The annealing in the pressurizedatmosphere is hereinafter referred to as “pressure annealing”. Thepressure annealing may be performed not only during post-annealing butalso during sintering.

A dielectric capacitor according to further aspect of the presentinvention comprises a lower electrode, a film of the ceramic of thepresent invention which is formed on the lower electrode, and an upperelectrode formed on the ceramic film. The ceramic may be applied tovarious types of devices of the dielectric capacitor.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view showing a high-dielectric/ferroelectriccapacitor formed by using a high-dielectric thin film of the presentinvention.

FIG. 2 is a view showing an XRD pattern of a ferroelectric BITcontaining Si of the present invention.

FIG. 3 is a view showing D-E hysteresis characteristics of aferroelectric BIT including Si or Si and Ge of the present invention.

FIG. 4 is a view showing XRD patterns after subjecting a ferroelectriccapacitor using the ferroelectric BIT including Si or Si and Ge of thepresent invention to pressure annealing at 500° C. for 30 min. whilechanging the oxygen partial pressure from 2 to 9.9 atm.

FIG. 5 is a view showing leakage characteristics after subjecting theferroelectric capacitor using the ferroelectric BIT including Si or Siand Ge of the present invention to pressure annealing at 500° C. for 30min. while changing the oxygen partial pressure from 2 to 9.9 atm.

FIG. 6 is a view showing surface morphology of conventional BIT and aBLST thin film of the present invention before and after pressureannealing.

FIG. 7 is a view showing surface morphology of the BLST thin film andBLSGT thin film of the present invention before and after pressureannealing.

FIG. 8 is a view showing electron diffraction patterns of BLST beforeand after pressure annealing.

FIG. 9 is a view showing XPS diffraction patterns of BLST before andafter pressure annealing.

FIG. 10 is a view showing reduction resistance of a BLST capacitor afterpressure annealing.

FIG. 11 is a view showing XRD patterns when changing the number of molesof a paraelectric for 1 mol of a ferroelectric.

FIG. 12 is a view showing hysteresis characteristics when the number ofmoles of the paraelectric is in the range of 0.1≦R≦1 for 1 mol of theferroelectric.

FIG. 13 is a view showing hysteresis characteristics when the number ofmoles of the paraelectric is in the range of 1≦R≦9 for 1 mol of theferroelectric.

FIG. 14 is a view showing TEM cross-sectional images of a ferroelectricthin film when changing the pressure of pressure annealing.

FIG. 15 is a view showing XRD patterns showing a film orientation whenusing a DLC (diamond-like carbon) buffer layer for the ferroelectricBLSGT thin film of the present invention.

FIG. 16 is a view showing hysteresis characteristics of a ferroelectriccapacitor formed by mixing various catalytic compounds withferroelectric BIT.

FIG. 17 is a view showing hysteresis characteristics of a ferroelectriccapacitor formed by mixing various catalytic compounds withferroelectric SBT.

FIG. 18 is a view showing hysteresis characteristics of a ferroelectriccapacitor formed by mixing various catalytic compounds withferroelectric PZT.

FIG. 19 is a view showing ferroelectric characteristics of aCaBi₄Ti₃Si_(0.5)Ge_(0.5)O₁₅ thin film of the present invention.

FIG. 20 is a view showing ferroelectric characteristics of anSr₂(Ta_(0.5),Nb_(0.25),Si_(0.125),Ge_(0.125))₂O₇ thin film of thepresent invention.

FIG. 21 is a view showing an XRD pattern of a Bi₂Sr₂Ca₂Cu₃O_(X)+BSO+BGOsuperconducting thin film of the present invention.

FIG. 22 is a view showing an MOCVD apparatus used for forming aferroelectric thin film of the present invention.

FIG. 23 is a view showing an XRD pattern of a TSO-BGO-BST thin film ofthe present invention.

FIG. 24 is a view showing a TEM cross-sectional image of the TSO-BGO-BSTthin film of the present invention.

FIG. 25 is a view showing a relation between a relative dielectricconstant and a frequency of the TSO-BGO-BST thin film of the presentinvention.

FIG. 26 is a view showing a relation between an applied voltage and theamount of stored charge of the TSO-BGO-BST thin film of the presentinvention.

FIG. 27 is a view showing leakage current characteristics of theTSO-BGO-BST thin film of the present invention.

FIG. 28 is a view showing an LSMCD apparatus using supercritical carriergas used for forming a ferroelectric thin film of the present invention.

FIG. 29 is a view showing a relation between a relative dielectricconstant and a frequency of the TSO-BGO-BST thin film of the presentinvention formed by using the LSMCD apparatus using supercriticalcarrier gas before and after pressure annealing.

FIG. 30 is a view showing a high-frequency magnetron sputteringapparatus used for forming a ferroelectric thin film of the presentinvention.

FIG. 31 is a cross-sectional view showing a BSO-BGO-SBT target of thepresent invention.

FIG. 32 is a view showing an XRD pattern of a BSO-BGO-SBT thin filmformed by using the high-frequency magnetron sputtering apparatus.

FIG. 33 is a view showing a TEM cross-sectional image of the BSO-BGO-SBTthin film formed by using the high-frequency magnetron sputteringapparatus.

FIG. 34 is a view showing hysteresis characteristics of the BSO-BGO-SBTthin film formed by using the high-frequency magnetron sputteringapparatus.

FIG. 35 is a view showing an XRD pattern of a BSO-BIT thin film formedby using a solid phase method.

FIG. 36 is a view showing hysteresis characteristics of the BSO-BIT thinfilm formed by using the solid phase method.

FIG. 37 is a cross-sectional view schematically showing a ferroelectricmemory device.

FIG. 38 is a cross-sectional view schematically showing an apparatus forforming a raw material body on a substrate by using an LSMCD method.

FIGS. 39A to 39C are conceptual views schematically showing amanufacturing process for a first multilayer ceramic film.

FIGS. 40A to 40C are conceptual views schematically showing amanufacturing process for a second multilayer ceramic film.

FIGS. 41A to 41C are conceptual views schematically showing amanufacturing process for a third multilayer ceramic film.

FIGS. 42A and 42B are conceptual views schematically showing amanufacturing process for a fourth multilayer ceramic film.

FIG. 43 is a view showing a TEM image of an oxide ferroelectric thinfilm of the present invention after presintering.

FIG. 44 is a view showing EDX composition analysis results at a lower Ptelectrode grain boundary and in an Si substrate of an oxideferroelectric BLST capacitor of the present invention and a conventionalferroelectric BIT capacitor.

FIG. 45 is a view showing surface morphology of an oxide ferroelectricthin film of the present invention when Ge/Si is 0.1, 5, 10, or 15.

FIG. 46 is a view showing reduction resistance of an oxide ferroelectricthin film of the present invention when Ge/Si is 0.1, 5, 10, or 15.

FIG. 47 is a view showing surface morphology of an oxide ferroelectricthin film of the present invention when Sn/Si is 3, 6, or 9.

FIG. 48 is a view showing reduction resistance of an oxide ferroelectricthin film of the present invention when Sn/Si is 3, 6, or 9.

FIG. 49 is a view showing reduction resistance of an oxide ferroelectricthin film of the present invention when 1<(Ge+Sn)/Si≦10 and Ge/Sn is 1.2or 1.5.

FIG. 50 is a view showing an XRD pattern of a ferroelectric BITcontaining Si and Ge of the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS

Embodiments of the present invention are described below.

(A) A first method of manufacturing a ceramic film of the presentinvention comprises:

a step of forming a ceramic film by crystallizing a raw material body,

wherein the raw material body includes different types of raw materialsin a mixed state, and

wherein the different types of raw materials differ from one another inat least one of a crystal growth condition and a crystal growthmechanism in the crystallization of the raw materials.

The different types of raw materials differ from one another in at leastone of the crystal growth condition and the crystal growth mechanism inthe crystallization of the raw materials. Specifically, the rawmaterials are judged to be different depending on whether or not the rawmaterials differ from one another in at least one of the crystal growthcondition and the crystal growth mechanism.

One of the different types of raw materials is a complex oxide materialhaving an oxygen octahedral structure such as a perovskite material,Bi-layer structured material, superconducting oxide material, andtungsten bronze material, and the other raw material is a paraelectricmaterial such as a layered catalytic substance which includes Si or Siand Ge in the constituent elements.

As examples of the crystal growth condition and the crystal growthmechanism in the crystallization of the raw materials, a crystallizationtemperature, crystal nucleus formation temperature, crystal growthtemperature, crystal growth rate, crystal nucleus formation rate, sizeof crystal nuclei, crystallization method, and the like can be given.

Moreover, examples include a phenomenon in which the density of initialcrystal nuclei is increased by allowing a region in which one of the rawmaterials is crystallized before the other raw material to occur overthe entire film, thereby preventing abnormal growth of crystals toprovide good surface morphology.

In this embodiment, the raw material body includes the different typesof raw materials. Specifically, the raw material body includes at leasttwo types of raw materials. The different types of raw materials differfrom one another in at least one of the crystal growth condition and thecrystal growth mechanism in the crystallization of the raw materials.Therefore, one of the raw materials can be crystallized before the otherraw material and the other raw material can be crystallized in theopenings between crystals produced from the above raw material bycontrolling various conditions, for example. Specifically, the openingsbetween crystals produced from one of the raw materials can be filledwith crystals produced from the other raw material. Therefore, surfacemorphology of the ceramic film can be improved.

The different types of raw materials may be crystallized at the sametime by controlling various conditions. For example, the crystallizationtemperature can be adjusted by causing a metal element of the rawmaterial to be replaced with another element. This enables thecrystallization temperatures of the different types of raw materials tobe approximately the same. The different types of raw materials can becrystallized at the same time if the crystallization temperatures of thedifferent types of raw materials are approximately the same.

(B) A second method of manufacturing a ceramic film of the presentinvention comprises:

a step of forming a ceramic film by crystallizing a raw material body,

wherein the raw material body includes different types of raw materialsin a mixed state, and

wherein the different types of raw materials differ from one another ina crystal structure produced from the raw materials.

The different types of raw materials differ from one another in thecrystal structure produced from the raw materials. Specifically, the rawmaterials are judged to be different when the raw materials differ fromone another in the crystal structure of the crystals obtained from theraw materials.

When crystals obtained from the raw materials are expressed as(Bi₂O₂)²⁺(A_(m−1)B_(m)O_(3m+1))²⁻, crystals having a different crystalstructure have different values for m, different elements for A and B,and the like.

For example, when crystals obtained from the raw materials are expressedas (Bi₂O₂)²⁺(A_(m−1)B_(m)O_(3m+1))²⁻, crystals having a differentcrystal structure have either Si or Si and Ge for B.

In this embodiment, the different types of raw materials differ from oneanother in the crystal structures produced from the raw materials. Ifthe raw materials differ from one another in the crystal structure ofthe crystals obtained from the raw materials, the raw materials differfrom one another in the crystal growth condition and the crystal growthmechanism of the raw materials. Therefore, effects the same as in thefirst method of manufacturing a ceramic film of the present inventioncan be obtained.

(C) A third method of manufacturing a ceramic film of the presentinvention comprises:

a step of forming a ceramic film by crystallizing a raw material body,

wherein the raw material body includes different types of raw materialsin a mixed state, and

wherein the different types of raw materials are individuallycrystallized at least at an initial stage of crystallization.

The different types of raw materials are individually crystallized atleast at an initial stage of crystallization.

In the third method of manufacturing a ceramic film of the presentinvention, the different types of raw materials are individuallycrystallized at least at an initial stage of crystallization. Therefore,crystals produced from one of the raw materials can be grown in theopenings between crystals produced from the other raw material. As aresult, occurrence of openings between the crystals can be prevented,whereby the surface morphology is improved.

The first to third methods of manufacturing a ceramic film of thepresent invention may have any of the following features.

(a) The ceramic film may be a ferroelectric or a high dielectric.

(b) The ceramic film may be a paraelectric.

(c) The ceramic film may include a ferroelectric and a paraelectric in amixed state.

(d) At least two of the different types of raw materials may differ fromeach other in crystallization temperature in the crystallization of theraw materials.

(e) At least two of the different types of raw materials may differ fromeach other in crystal nucleus formation temperature in thecrystallization of the raw materials.

(f) At least two of the different types of raw materials may differ fromeach other in crystal growth temperature in the crystallization of theraw materials.

(g) At least two of the different types of raw materials may differ fromeach other in crystal growth rate in the crystallization of the rawmaterials.

(h) At least two of the different types of raw materials may differ fromeach other in crystal nucleus formation rate in the crystallization ofthe raw materials.

(i) At least two of the different types of raw materials may differ fromeach other in the size of crystal nuclei in the crystallization of theraw materials.

(j) At least two of the different types of raw materials may differ fromeach other in crystallization method in the crystallization of the rawmaterials.

(k) There may be a time lag between the crystallizations of thedifferent types of raw materials.

(l) There may be a time lag between the formation of crystal nuclei inthe crystallization of the raw materials.

(m) One of the raw materials crystallized first may have a catalyticeffect for the other raw material crystallized later.

(n) The different types of raw materials may be crystallized at the sametime.

(o) The different types of raw materials may be compound-crystallized atthe same time.

(p) The different types of raw materials may be dissolved at the sametime.

When crystallizing the different types of raw materials at the sametime, crystals produced from one of the raw materials interrupt thegrowth of crystals produced from the other raw material. As a result,the resulting crystals can be microcrystallized. This causes theopenings between the crystals to become narrow, whereby the surfacemorphology is improved.

When crystallizing the different types of raw materials at the sametime, it is preferable to use raw materials which produce a ceramichaving a different crystal structure. This enables the crystal growthconditions and the crystal growth mechanism during crystallization ofthe raw materials to be changed at the same time.

(q) When ceramics obtained from the raw materials are expressed as(Bi₂O₂)²⁺(A_(m−1)B_(m)O_(3m+1))²⁻, the different types of raw materialsmay have different values for m.

(r) One of the different types of raw materials may be a complex oxidematerial having an oxygen octahedral structure such as a perovskite andbismuth-layer structured oxide material shown by ABO₃ or(Bi₂O₂)²⁺(A_(m−1)B_(m)O_(3m+1))²⁻ (wherein A represents at least oneelement selected from the group consisting of Li, Na, K, Rb, Pb, Ca, Sr,Ba, Bi, La, and Hf, B represents at least one element selected from thegroup consisting of Ru, Fe, Ti, Zr, Nb, Ta, V, W, and Mo, and m is anatural number of 5 or less), a superconducting oxide material shown byLanBa₂Cu₃O₇, Trm₂Ba₂Ca_(n−1)Cu_(n)O_(2n+4), orTrmBa₂Ca_(n−1)Cu_(n)O_(2n+3) (wherein Lan represents at least one ionselected from the group consisting of Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd,Tb, Dy, Ho, Er, Tm, Yb, and Lu, Trm represents at least one ion selectedfrom the group consisting of Bi, Tl, and Hg, and m is a natural numberfrom 1 to 5), and a tungsten bronze structured material shown byA_(0.5)BO₃ (tetragonal bronze structure) or A_(0.3)BO₃ (hexagonal bronzestructure) (wherein A represents at least one element selected from thegroup consisting of Li, Na, K, Rb, Cs, Pb, Ca, Sr, Ba, Bi, and La, and Brepresents at least one element selected from the group consisting ofRu, Fe, Ti, Zr, Nb, Ta, V, W, and Mo), and the other raw material may bea paraelectric material formed of a mixture of at least one oxideselected from the group consisting of CaO, BaO, PbO, ZnO, MgO, B₂O₃,Al₂O₃, Y₂O₃, La₂O₃, Cr₂O₃, Bi₂O₃, Ga₂O₃, ZrO₂, TiO₂, HfO₂, NbO₂, MoO₃,WO₃, and V₂O₅, and SiO₂ or SiO₂ and GeO₂.

(s) The raw material body may be formed on a substrate by using a liquidsource misted chemical deposition (LSMCD) method.

In the case of forming the raw material body on the substrate by usingthe LSMCD method, the raw material body is provided to the substrate inthe form of a mist by ultrasonic waves. This improves mixing conditionsfor the different types of raw materials. Therefore, a ceramic filmhaving microcrystals can be obtained.

The raw material body may be formed on a substrate by separatelyproviding the different types of raw materials.

The raw material body may be formed on a substrate by providing thedifferent types of raw materials at the same time.

(t) The raw material body may be formed on a substrate by spin coatingor dipping.

(u) The raw material body may be formed on a substrate by ametal-organic chemical vapor deposition (MOCVD) method.

(v) The raw material body may be formed on a substrate by sputtering orlaser ablation.

(w) The raw material body may be formed on a substrate by a solid phasemethod.

(x) The raw materials may be at least one of a sol-gel raw material andan MOD raw material.

(y) The raw material body may include a sol-gel raw material and an MODraw material.

In the above (x) and (y), the sol-gel raw material may be polycondensedby hydrolysis.

In the above (x) and (y), the sol-gel raw material may be complexpolymerized by hydrolysis.

The sol-gel raw material may have a crystal structure similar to thecrystal structure of crystals obtained by crystallizing the rawmaterial. This enables the sol-gel raw material to be easilycrystallized.

The MOD raw material may be a polynuclear complex raw material.

The raw material body may include different types of sol-gel rawmaterials, and the different types of sol-gel raw materials may differfrom one another in the degree of polycondensation or metal elementcomposition.

The raw material body may include different types of sol-gel rawmaterials, and the different types of sol-gel raw materials may not bemixed at an atomic level or a molecular level.

The term “mixed at an atomic level” means that atoms which make up theraw materials are mixed, for example. Specifically, the raw materialsare preferably mixed in a state in which individual molecules oraggregates are maintained. If the raw materials are not mixed at anatomic level or a molecular level, the effects of the present inventioncan be obtained reliably. Moreover, characteristics of the ceramic filmcan be further improved.

Specifically, the sol-gel raw material is in a state in which a longpolycondensed organic metal network is dispersed in a solvent. This aimsat bringing constituent elements of an objective oxide close to oneanother in advance. The MOD raw material is in a state in which theconstituent elements of an objective oxide are dispersed without beingbonded to one another. The feature in which the raw material body of thepresent invention includes the different types of sol-gel raw materials,and the different types of sol-gel raw materials are not mixed at anatomic level or a molecular level means as follows. The constituentelements of the sol-gel raw material for a ferroelectric form a network.The constituent elements of the sol-gel raw material for a paraelectricalso form a network. However, these networks are not polycondensed andhave a relation similar to that of the constituent elements in the MODraw material. Specifically, these networks are not mixed at an atomiclevel or a molecular level. This enables each of the objective oxides tobe formed separately.

(D) A fourth method of manufacturing a ceramic film of the presentinvention comprises:

a step of forming a ceramic film by crystallizing a raw material body,

wherein the raw material body is crystallized so that a plurality ofphases is formed.

The ceramic film may have any of the following features.

(a) The ceramic film may be a ferroelectric or a high dielectric.

(b) The ceramic film may be a paraelectric.

(c) The ceramic film may include a ferroelectric and a paraelectric in amixed state.

(E) A fifth method of manufacturing a ceramic film of the presentinvention comprises:

a step of forming a ceramic film by crystallizing a ceramic raw materialliquid which includes a first raw material liquid and a second rawmaterial liquid, or a vaporized raw material gas of the ceramic rawmaterial liquid,

wherein the first raw material liquid and the second raw material liquidare different types of liquids,

wherein the first raw material liquid is a raw material liquid forproducing a ferroelectric including a perovskite material, Bi-layerstructured material, superconducting oxide material, and tungsten bronzematerial, and

wherein the second raw material liquid is a raw material liquid forproducing a layered catalytic oxide in which Si or Si and Ge areprovided in the B site.

A ferroelectric film having specific characteristics at a lowtemperature can be formed by forming a ceramic film using the ceramicraw material liquid of the present invention. A ceramic film obtained byusing the ceramic raw material liquid of the present invention hasexcellent surface morphology.

If the molar ratio of a ferroelectric produced from the first rawmaterial liquid to a paraelectric oxide produced from the second rawmaterial liquid (complex oxide material/paraelectric material) is 1 ormore, a ferroelectric ceramic film can be formed by crystallizing theraw material body.

If the molar ratio of a ferroelectric produced from the first rawmaterial liquid to a paraelectric oxide produced from the second rawmaterial liquid (complex oxide material/paraelectric material) is lessthan 1, a ceramic film including a ferroelectric and a paraelectric in amixed state can be formed by crystallizing the raw material body.

This enables formation of a ceramic film which is formed of a mixture ofa ferroelectric material having an oxygen octahedral structure producedfrom the first raw material liquid and a paraelectric material having anoxygen tetrahedral structure consisting of SiO₂ or a mixture of SiO₂ andGeO₂ in the crystal structure produced from the second raw materialliquid, and which maintains a relative dielectric constant of theferroelectric and does not shows hysteresis after mixing andcrystallizing the complex oxide material and the paraelectric material.

If the molar ratio of a ferroelectric produced from the first rawmaterial liquid to a paraelectric oxide produced from the second rawmaterial liquid (complex oxide material/paraelectric material) is lessthan 1, a ferroelectric ceramic film including a ferroelectric and aparaelectric in a mixed state can be formed by crystallizing the rawmaterial body.

This enables formation of a ceramic film which is formed of a mixture ofa ferroelectric material having an oxygen octahedral structure producedfrom the first raw material liquid and a paraelectric material having anoxygen tetrahedral structure consisting of SiO₂ or a mixture of SiO₂ andGeO₂ in the crystal structure produced from the second raw materialliquid, and which does not show changes in the Curie temperature of theferroelectric material after mixing and crystallizing the complex oxidematerial and the paraelectric material.

A ferroelectric ceramic film orientated in an optional direction can beformed by providing DLC for determining the growth direction of thefifth ceramic film of the present invention at the interface with thesubstrate when crystallizing the ceramic film.

The first raw material liquid may be a solution in which a metalcompound or a metal-inorganic compound of a metal element for theferroelectric is dissolved in a solvent, and the second raw materialliquid may be a solution in which a metal compound or a metal-inorganiccompound of a metal element for the layered catalytic oxide is dissolvedin a solvent.

(F) A sixth method of manufacturing a ceramic film of the presentinvention comprises:

wherein an uppermost raw material layer in the raw material body layerhas a crystallization temperature lower than the crystallizationtemperature of a lower raw material layer which is in contact with theuppermost raw material layer.

According to this embodiment, crystals produced from the uppermost rawmaterial layer function as a seed layer during crystallization of thelower raw material layer. Moreover, since crystals obtained from theuppermost raw material layer have no layered structure, the surfacemorphology of the ceramic film can be improved.

The lower raw material layer which is in contact with the uppermost rawmaterial layer may be formed on a substrate with a first raw materiallayer interposed therebetween, and the first raw material layer may havea crystallization temperature lower than the crystallization temperatureof the lower raw material layer which is in contact with the uppermostraw material layer. Therefore, crystals produced from the first rawmaterial layer function as a seed layer during crystallization of thelower raw material layer which is in contact with the uppermost rawmaterial layer.

(G) A seventh method of manufacturing a ceramic film of the presentinvention comprises:

a step of forming a raw material body layer which includes a rawmaterial laminate in which a first raw material layer, a second rawmaterial layer, and a third raw material layer are layered in thatorder, and

a step of forming a ceramic film by crystallizing the raw material bodylayer,

wherein the second raw material layer has a crystallization temperaturelower than crystallization temperatures of the first and third rawmaterial layers.

According to this embodiment, crystals produced from the second rawmaterial layer function as a stopper for preventing the growth ofcrystals in the first raw material layer and the third raw materiallayer.

Therefore, the grain size of the crystals produced from the first rawmaterial layer and the third raw material layer can be reduced.

A fourth raw material layer may be further layered on the third rawmaterial layer, and the fourth raw material layer may have acrystallization temperature lower than the crystallization temperatureof the third raw material layer. In this case, crystals produced fromthe fourth raw material layer function as a seed layer duringcrystallization of the third raw material layer.

(J) A tenth method of manufacturing a ceramic film of the presentinvention comprises:

a step of forming a raw material body layer in which a plurality of rawmaterial layers is layered, and

a step of forming a ceramic film by crystallizing the raw material bodylayer,

wherein an uppermost raw material layer in the raw material body layerhas a crystallization temperature higher than the crystallizationtemperature of a lower raw material layer which is in contact with theuppermost raw material layer.

According to this embodiment, crystals produced from the uppermost rawmaterial layer can be formed to cover crystals produced from the lowerraw material layer.

The crystals obtained from the uppermost raw material layer in the rawmaterial body layer preferably have no layered structure. This enablesthe surface morphology of the ceramic film to be improved.

In the first to eighth methods of manufacturing a ceramic film of thepresent invention, the step of forming a ceramic film by crystallizingthe raw material body may be performed two or more times.

Ceramic Film

(A) A first ceramic film of the present invention is obtained by amethod of manufacturing a ceramic film of the present invention.

(B) A second ceramic film of the present invention comprises:

a laminate in which a first crystal layer and a second crystal layer arelayered in that order,

wherein the second crystal layer has a melting point lower than themelting point of the first crystal layer, and

wherein crystals in the second crystal layer do not have a layeredstructure.

In this embodiment, a region in which a constituent metal element of thefirst crystal layer and a constituent metal element of the secondcrystal layer are mixed may be present near the interface between thefirst crystal layer and the second crystal layer.

In this embodiment, the first crystal layer may be formed on a substratewith a third crystal layer interposed therebetween, and the thirdcrystal layer may have a melting point lower than the melting point ofthe first crystal layer.

(C) A third ceramic film of the present invention comprises:

a crystal laminate in which a first crystal layer, a second crystallayer, and a third crystal layer are layered in that order,

wherein the second crystal layer has a melting point lower than meltingpoints of the first crystal layer and the third crystal layer.

In this embodiment, a region in which a constituent metal element of thefirst crystal layer and a constituent metal element of the secondcrystal layer are mixed may be present near the interface between thefirst crystal layer and the second crystal layer, and a region in whicha constituent metal element of the second crystal layer and aconstituent metal element of the third crystal layer are mixed may bepresent near the interface between the second crystal layer and thethird crystal layer.

In this embodiment, a fourth crystal layer may be formed on the thirdcrystal layer, the fourth crystal layer may have a melting point lowerthan the melting point of the third crystal layer, and a region in whicha constituent metal element of the third crystal layer and a constituentmetal element of the fourth crystal layer are mixed may be present nearthe interface between the third crystal layer and the fourth crystallayer.

(D) A fourth ceramic film of the present invention comprises:

a laminate in which a first crystal layer and a second crystal layer arelayered in that order,

wherein the second crystal layer has a melting point higher than themelting point of the first crystal layer, and

wherein crystals in the second crystal layer do not have a layeredstructure.

In this embodiment, a region in which a constituent metal element of thefirst crystal layer and a constituent metal element of the secondcrystal layer are mixed may be present near the interface between thefirst crystal layer and the second crystal layer.

Application example of ceramic film

A semiconductor device of the present invention comprises a capacitorincluding a ceramic film of the present invention.

An element of the present invention comprises the ceramic film of thepresent invention.

The present invention further provides a ferroelectric capacitor and amethod of manufacturing a ceramic film given below.

A ferroelectric capacitor of the present invention comprises:

a lower electrode, a ceramic film which includes first crystals andsecond crystals and is formed on the lower electrode, and an upperelectrode formed on the ceramic film,

wherein the first crystals include a perovskite material, Bi-layerstructured material, superconducting oxide material, and tungsten bronzestructure,

wherein the second crystals are a paraelectric oxide having an oxygentetrahedral structure consisting of SiO₂ or a mixture of SiO₂ and GeO₂in the structure, and

wherein the first crystals are intermittently formed in the planardirection of the ceramic film, and the second crystals are formed so asto be interposed between the first crystals.

The ceramic film which makes up the ferroelectric capacitor may beformed by a first method given below.

The first method comprises:

a step of forming a ceramic film by crystallizing a ceramic raw materialliquid which includes a first raw material liquid and a second rawmaterial liquid,

wherein the first raw material liquid and the second raw material liquidare different types of liquids,

wherein the first raw material liquid is a raw material liquid forproducing a perovskite material, Bi-layer structured material,superconducting oxide material, and ferroelectric having a tungstenbronze structure, the second raw material liquid is a raw materialliquid for producing a layered catalytic oxide in which Si or Si and Geare provided in the B site,

wherein a solvent included in the first raw material liquid and asolvent included in the second raw material liquid have differentpolarities, and

wherein first crystals produced from the first raw material liquid areintermittently formed in the planar direction of the ceramic film, andsecond crystals produced from the second raw material liquid are formedso as to be interposed between the first crystals by depositing theceramic film in a state in which the first raw material liquid and thesecond raw material liquid are phase separated.

The ceramic film which makes up the ferroelectric capacitor may beformed by a second method given below.

The second method comprises:

a step of forming a ceramic film by crystallizing a ceramic raw materialliquid including a first raw material liquid and a second raw materialliquid,

wherein the first raw material liquid and the second raw material liquidare different types of liquids,

wherein the first raw material liquid is a raw material liquid forproducing a perovskite material, Bi-layer structured material,superconducting oxide material, and ferroelectric including a tungstenbronze structure, the second raw material liquid is a raw materialliquid for producing a layered catalytic oxide in which Si or Si and Geare provided in the B site,

wherein a solvent included in the first raw material liquid and asolvent included in the second raw material liquid have differentpolarities, and

wherein first crystals produced from the first raw material liquid areintermittently formed in the planar direction of the ceramic film, andsecond crystals produced from the second raw material liquid are formedso as to be interposed between the first crystals by forming a mist ofthe first raw material liquid so as to be dispersed on a substrate, andforming a film of the second raw material liquid on the substrate.

In the second method, as the method for forming the film of the secondraw material liquid on the substrate on which the mist produced from thefirst raw material liquid is dispersed, a method of forming the film ina state in which the second raw material liquid is misted, or a methodof forming the film of the second raw material liquid by spin coatingmay be used. These methods also apply to a second method describedlater.

The first and second methods may have the following features. Thesefeatures also applied to first and second methods described later.

(a) One of the solvents included in the first raw material liquid andthe second raw material liquid may be soluble in water, and the othersolvent may be insoluble in water.

(b) The molar ratio of the ferroelectric produced from the first rawmaterial liquid to the ABO-type oxide produced from the second rawmaterial liquid may be from 100:20 to 100:100.

(c) The first raw material liquid may be a solution in which a metalcompound or a metal inorganic compound of a metal element for theferroelectric is dissolved in a solvent, and

the second raw material liquid may be a solution in which a metalcompound or a metal inorganic compound of a metal element for thelayered catalytic oxide in which Si or Si and Ge are provided in the Bsite is dissolved in a solvent.

A ferroelectric capacitor of the present invention comprises:

a lower electrode, a ceramic film which includes first crystals andsecond crystals and is formed on the lower electrode, and an upperelectrode formed on the ceramic film,

wherein the first crystals include a perovskite material, Bi-layerstructured material, superconducting oxide material, and tungsten bronzestructure,

wherein the second crystals are a layered catalytic oxide in which Si,or Si and Ge are provided in the B site, and

wherein the first crystals are intermittently formed in the planardirection of the ceramic film, and the second crystals are formed so asto be interposed between the first crystals.

The ceramic which makes up the ferroelectric capacitor may be formed bya method similar to the above first and second methods.

Specifically, a first method comprises:

a step of forming a ceramic film by crystallizing a ceramic raw materialliquid which includes a third raw material liquid and a fourth rawmaterial liquid,

wherein the third raw material liquid and the fourth raw material liquidare different types of liquids,

wherein the third raw material liquid is a raw material liquid forproducing a perovskite material, Bi-layer structured material,superconducting oxide material, and tungsten bronze type ferroelectric,

wherein the fourth raw material liquid is a raw material liquid forproducing a layered catalytic oxide in which Si or Si and Ge areprovided in the B site,

wherein a solvent included in the third raw material liquid and asolvent included in the fourth raw material liquid have differentpolarities, and

wherein third crystals produced from the third raw material liquid areintermittently formed in the planar direction of the ceramic film, andfourth crystals produced from the fourth raw material liquid are formedso as to be interposed between the third crystals by depositing theceramic film in a state in which the third raw material liquid and thefourth raw material liquid are phase separated.

A second method comprises:

a step of forming a ceramic film by crystallizing a ceramic raw materialliquid which includes a third raw material liquid and a fourth rawmaterial liquid,

wherein the third raw material liquid and the second raw material liquidare different types of liquids,

wherein the third raw material liquid is a raw material liquid forproducing a perovskite material, Bi-layer structured material,superconducting oxide material, and tungsten bronze type ferroelectric,

wherein the fourth raw material liquid is a raw material liquid forproducing a layered catalytic oxide in which Si or Si and Ge areprovided in the B site,

wherein a solvent included in the third raw material liquid and asolvent included in the fourth raw material liquid have differentpolarities, and

wherein third crystals produced from the third raw material liquid areintermittently formed in the planar direction of the ceramic film, andfourth crystals produced from the fourth raw material liquid are formedso as to be interposed between the third crystals by forming a mist ofthe third raw material liquid so as to be dispersed on a substrate, andforming a film of the fourth raw material liquid on the substrate.

In the second method, as the method of forming the film of the fourthraw material liquid on the substrate on which the mist produced from thethird raw material liquid is dispersed, a method of forming the film ina state in which the fourth raw material liquid is misted, or a methodof forming the film of the fourth raw material liquid by spin coatingmay be used.

The first and second methods may have the following features.

(a) One of the solvents included in the third raw material liquid andthe fourth raw material liquid may be soluble in water, and the othersolvent may be insoluble in water.

(b) The molar ratio of the ferroelectric produced from the third rawmaterial liquid to the ABO-type oxide produced from the fourth rawmaterial liquid may be from 100:20 to 100:100.

(c) The third raw material liquid may be a solution in which a metalcompound or a metal-inorganic compound of a metal element for theferroelectric is dissolved in a solvent, and the fourth raw materialliquid may be a solution in which a metal compound or a metal-inorganiccompound of a metal element for the layered catalytic oxide is dissolvedin a solvent.

A ferroelectric capacitor of the present invention comprises:

a lower electrode, a ceramic film which includes first crystals andsecond crystals and is formed on the lower electrode, and an upperelectrode formed on the ceramic film,

wherein the first crystals are intermittently formed in the planardirection of the ceramic film, and the second crystals are formed so asto be interposed between the first crystals.

A first method for forming the ceramic film which makes up theferroelectric capacitor comprises:

a step of forming a ceramic film by crystallizing a ceramic raw materialliquid which includes a first raw material liquid and a second rawmaterial liquid,

wherein the first raw material liquid and the second raw material liquidare different types of liquids,

wherein the first raw material liquid is a raw material liquid forproducing a ferroelectric,

wherein the second raw material liquid is a raw material liquid forproducing a layered catalytic oxide,

wherein a solvent included in the first raw material liquid and asolvent included in the second raw material liquid have differentpolarities, and

wherein first crystals produced from the first raw material liquid areintermittently formed in the planar direction of the ceramic film, andsecond crystals produced from the second raw material liquid are formedso as to be interposed between the first crystals by depositing theceramic film in a state in which the first raw material liquid and thesecond raw material liquid are phase separated.

A second method for forming the ceramic film which makes up theferroelectric capacitor comprises:

a step of forming a ceramic film by crystallizing a ceramic raw materialliquid which includes a first raw material liquid and a second rawmaterial liquid,

wherein the first raw material liquid and the second raw material liquidare different types of liquids,

wherein the first raw material liquid is a raw material liquid forproducing a ferroelectric, and the second raw material liquid is a rawmaterial liquid for producing a layered catalytic oxide in which Si orSi and Ge are provided in the B site,

wherein a solvent included in the first raw material liquid and asolvent included in the second raw material liquid have differentpolarities, and

wherein first crystals produced from the first raw material liquid areintermittently formed in the planar direction of the ceramic film, andsecond crystals produced from the second raw material liquid are formedso as to be interposed between the first crystals by forming a mist ofthe first raw material liquid so as to be dispersed on a substrate, andforming a film of the second raw material liquid on the substrate.

There are no specific limitations to the first raw material liquid andthe second raw material liquid insofar as the liquids have the aboveconfiguration. Various types of combinations are possible. Specifically,the manufacturing methods may be applied not only to the case of theabove-described ferroelectric having a Bi-type layered perovskitestructure or a PZT-type perovskite structure, but also to the case wherethe first raw material liquid is a raw material liquid for producing aperovskite material, Bi-layer structured material, superconducting oxidematerial, and tungsten bronze type ferroelectric,

the fourth raw material liquid is a raw material liquid for producing alayered catalytic oxide in which Si or Si and Ge are provided in the Bsite, and the second raw material liquid is a raw material liquid forproducing a layered catalytic oxide in which Si or Si and Ge areprovided in the B site.

According to the above first and second methods, the first crystalsproduced from the first or third raw material liquid are intermittentlyformed in the planar direction of the ceramic film, and the secondcrystals produced from the second or fourth raw material liquid areformed so as to be interposed between the first crystals. This causesthe second crystals (paraelectric, for example) to be disposed tosurround the first crystals (ferroelectric, for example). In such astructure, occurrence of domains in the direction at an angle of 90°with respect to the direction of the thickness of the ferroelectric filmof the ferroelectric capacitor formed by the upper and lower electrodesand the ferroelectric (generally called 90° domains) can be prevented.As a result, squareness of the hysteresis characteristics of theferroelectric capacitor can be improved.

A ceramic of the present invention is a complex oxide having an oxygenoctahedral structure, and comprises Si and Ge in the oxygen octahedralstructure. The ceramic of the present invention may be referred to as aceramic in which a paraelectric including Si and Ge is dissolved in acomplex oxide having an oxygen octahedral structure. Si and Ge includedin such an oxygen octahedral structure have a coordination number ofsix.

The ceramic of the present invention is obtained by replacing metalcations (B site ions) positioned in the oxygen octahedral structure ofthe complex oxide with an Si ion and a Ge ion. For example, a(Bi,La)₄(Ti,Si,Ge)₃O₁₂ ferroelectric of the present invention isobtained by replacing the B site ions with Si⁴⁺ and Ge⁴⁺. Such a(Bi,La)₄(Ti,Si,Ge)₃O₁₂ structure cannot be easily known from the analogyto Bi₄Ti₃O₁₂. Specifically, Si⁴⁺ and Ge⁴⁺ have strong covalent bondingproperties and are not metal elements. Moreover, it is a common practiceto replace an element which makes up a perovskite by using an ion havingan ionic radius close to that of the element. However, Si⁴⁺ has an ionicradius of 0.26 angstrom, which is extremely smaller than the ionicradius of Ti⁴⁺ ⁽0.6 angstrom). Therefore, it is difficult to consider toreplace the B site ions with Si⁴⁺ and Ge⁴⁺. Because of this, the presentinvention overthrows the common knowledge of a conventionalferroelectric material. The ferroelectric material of the presentinvention completely differs from a conventional ferroelectric material.

Formation of the ceramic of the present invention is remarkablyfacilitated by replacing part of the B sites of the oxygen octahedronwith Si and Ge. Since the ionic radius of Ge is larger than that of Siand close to the lattice spacing of the B site, Ge has remarkably highcapability of replacing the B site of the oxygen octahedron incomparison with Si. Since the entire lattice of the oxygen octahedronshrinks or is distorted when Ge enters the B site of the oxygenoctahedron, Si easily replaces the B site. In this case, it is importantto use Si and Ge at the same time. This is because the introduction ofcovalent bonding properties into the oxygen octahedron is insufficientonly by using Ge, whereby the catalytic function of the paraelectric isinsufficient.

The molar ratio of Ge to Si in the ceramic of the present invention ispreferably 0<Ge/Si≦10, and still more preferably 0<Ge/Si≦1.

If the ratio of Ge to Si is within the specific range, good surfacemorphology, crystallinity, and interface can be obtained. In particular,if the ratio is 0<Ge/Si≦1, covalent bonding properties are increased dueto a high percentage of Si having a small ionic radius, whereby thereduction resistance is remarkably improved. If the ratio is 0<Ge/Si≦10,since Ge is the same group element as Si and has a large ionic radiusfor one period, Ge is easily added to the oxygen octahedral structure,whereby the thin film of the present invention can be easily formed.Since Ge has an ionic radius significantly smaller than that of the Bsite ion of a conventional ferroelectric, sufficient covalent bondingproperties are provided in comparison with a conventional ferroelectric.The covalent bonding properties are decreased for an increase in ionicbonding properties in comparison with the case of using only Si.

When the ratio is 10<Ge/Si, the surface morphology deteriorates as theratio of Ge to Si is increased, as shown in FIG. 45. The surfacemorphology significantly deteriorates when Ge/Si=15. When subjected to aheat treatment for 10 minutes in a 3% H₂ atmosphere, not only thesurface morphology becomes rough, but also the reduction resistancesignificantly deteriorates, as shown in FIG. 46.

In the above example, formation of the thin film of the presentinvention can be further facilitated by using Sn instead of Ge, since Snis easily added to the oxygen octahedral structure for a furtherincrease in the ionic radius. In this case, the ratio of Sn to Si is0<Sn/Si<9. If the ratio is 9≦Sn/Si, the surface morphology significantlydeteriorates as shown in FIG. 47. Moreover, reduction resistancesignificantly deteriorates when subjected to a heat treatment for 10minutes in a 3% H₂ atmosphere, as shown in FIG. 48.

When part of the Ge is replaced with Sn so that 1<(Ge+Sn)/Si≦10(Ge/Sn≦1.2), reduction resistance is improved in comparison with thecase of using Si and Sn when subjected to a heat treatment for 10minutes in a 3% H₂ atmosphere, as shown in FIG. 49.

The complex oxide having the oxygen octahedral structure may be at leastone oxide selected from a perovskite, bismuth-layer structured oxide,superconducting oxide, and tungsten bronze structured oxide, and theparaelectric may be a layered catalytic substance which includes Si andGe in the constituent elements.

The ceramic of the present invention may be a complex oxide having anoxygen octahedral structure, and comprise a ferroelectric layer whichincludes Si or Si and Ge, and a paraelectric layer having an oxygentetrahedral structure which includes Si or Si and Ge in the constituentelements in the oxygen octahedral structure, wherein at least one of theferroelectric layer and the paraelectric layer may have a column-shapedstructure extending in the direction of the film thickness. In thiscase, the layer having the column-shaped structure may have a diameterof 1 to 50 nm.

The present inventors have found that, when the number of moles of thelayered catalytic compound is relatively larger than that of the complexoxide having an oxygen octahedron, an excess layered catalytic compoundis separated from the complex oxide having an oxygen octahedron in thedirection of the film thickness. Therefore, characteristics such asferroelectric characteristics can optionally be set by controlling theamount of the layered catalytic compound to be added.

The mixing ratio of the complex oxide material to the paraelectricmaterial (complex oxide material/paraelectric material) is set takinginto consideration the above characteristics such as ferroelectriccharacteristics. For example, if the molar ratio of the complex oxidematerial to the paraelectric material is 1 or more, characteristics canbe controlled by optionally changing the material characteristics of thecomplex oxide material such as a remanent polarization in the case ofusing a ferroelectric material. If the molar ratio of the complex oxidematerial to the paraelectric material is less than 1, the surfacemorphology, crystallinity, and reduction resistance can be improvedwithout changing the material characteristics of the complex oxidematerial such as a remanent polarization in the case of using aferroelectric material.

If at least one of the ferroelectric layer and the paraelectric layerhas the column-shaped structure, second crystals (paraelectric, forexample) are disposed to surround first crystals (ferroelectric, forexample). In such a structure, occurrence of domains in the direction atan angle of 90° with respect to the direction of the thickness of theferroelectric film of the ferroelectric capacitor (generally called 90°domains) can be prevented. As a result, squareness of the hysteresischaracteristics of the ferroelectric capacitor can be improved.

A method of manufacturing a ceramic according to the present inventioncomprises forming a film which includes a complex oxide material havingan oxygen octahedral structure and a paraelectric material having acatalytic effect for the complex oxide material in a mixed state, andsubjecting the film to a heat treatment, wherein the paraelectricmaterial is a layered catalytic substance which includes Si in theconstituent elements or a layered catalytic substance which includes Siand Ge in the constituent elements.

According to the manufacturing method of the present invention, sinceinitial nuclei occur in the entire film in which the complex oxidematerial and the paraelectric material are present in a mixed state,coarse particles are rarely grown. Therefore, good surface morphologycan be obtained.

According to the manufacturing method of the present invention, covalentbonding properties are increased over the entire crystal lattice byintroducing Si and Ge into the oxygen octahedron of various types ofcomplex oxide materials having strong ionic bonding properties such as aperovskite material, bismuth-layer structured material, superconductingoxide material, and tungsten bronze material, whereby resistance toreduction due to hydrogen or the like is increased.

According to the manufacturing method of the present invention, a metalelement such as V or W, for which replacement in the crystal lattice isdifficult using a coating method such as spin coating, can be easilyreplaced.

The heat treatment may include sintering and post-annealing, wherein atleast the post-annealing may be performed in a pressurized atmospherecontaining at least either oxygen or ozone (hereinafter called “oxygenatmosphere”). The post-annealing is preferably performed in apressurized state such as at 2 atm. or more, and still more preferablyat 2 to 9.9 atm. The post-annealing may be performed after forming anelectrode on the film in which the complex oxide material and theparaelectric material are present in a mixed state.

The characteristics of the ceramic can be further stabilized andimproved by performing post-annealing in such a pressurized oxygenatmosphere.

Oxygen deficiency (shift of XRD peak to higher angle side) in thecomplex oxide material can be improved by performing pressure annealingin the oxygen atmosphere. Moreover, crystal growth characteristics andleakage current characteristics can be improved. As a result, goodferroelectric characteristics can be stably obtained.

The oxide thin film of the present invention is formed of a mixture offine crystal particles. Crystal growth is promoted by performingpressure annealing in oxygen at a comparatively low temperature, forexample, annealing at 500° C. and 9.9 atm. in a 100% oxygen atmosphere,whereby the structure of the thin film is close to a single crystalstructure. Specifically, crystals show behavior similar to epitaxialgrowth by pressure annealing in the oxygen atmosphere. It is known thatoxygen deficiency is improved by performing pressure annealing in aconventional complex oxide material. However, behavior similar toepitaxial growth is peculiar to the complex oxide material of thepresent invention which includes Si and Ge in the oxygen octahedron.

The heat treatment in the pressurized oxygen atmosphere has a sufficienteffect after crystallization. However, it is more effective to performthe heat treatment after providing an upper electrode taking intoconsideration the interface state between the film and the upperelectrode. In the present invention, processing can be performed in anamorphous state which enables easy processing and thermal damage to theelement can be minimized by performing crystallization in thepressurized oxygen atmosphere and formation of the upper electrode atthe same time.

As the paraelectric material, a compound having an effect of loweringthe crystallization temperature of the complex oxide material,specifically, a layered catalytic compound having a crystallizationtemperature lower than that of the ferroelectric is used.

The paraelectric material preferably includes Si or Si and Ge having acoordination number of four, and has an oxygen tetrahedral structure.Since the layered catalytic compound which includes Si and Ge in theconstituent elements has a low crystallization temperature and lowdensity, the layered catalytic compound has high catalytic action.Moreover, the layered catalytic compound has good lattice matching withmany oxide materials having an oxygen octahedron. Therefore, the layeredcatalytic compound which includes Si and Ge is first crystallized in thefilm, and the complex oxide material is crystallized on the surface ofthe layered catalytic compound by effectively utilizing the catalyticaction of the layered catalytic compound. Specifically, in the presentinvention, activation energy required for the crystallization of thecomplex oxide is reduced by using the layered catalytic compound,whereby the crystallization temperature is lowered. By lowering thecrystallization temperature, the applied energy can be effectiveutilized for compensation for oxygen deficiency and crystal growth.

Since the constituent elements of the layered catalytic compound of thepresent invention replace the A and B sites of the oxygen octahedrontherewith when the elements have finished the function as a catalyst,the layered catalytic compound does not essentially allow the layeredcatalytic compound structure to remain. As a result, since the layeredcatalytic compound is not formed to separate the film in the directionof the thickness, a decrease in ferroelectric characteristics andelectrical characteristics can be prevented.

In the manufacturing method of the present invention, a sol-gel rawmaterial may be used for at least one of the complex oxide material andthe paraelectric material. At least one of the complex oxide materialand the paraelectric material may be formed by using a complexpolymerization method.

In the manufacturing method of the present invention, the film in whichthe complex oxide material and the paraelectric material are present ina mixed state is formed by any of a solid phase method, coating method,LSMCD method, MOCVD method, and sputtering method. As the coatingmethod, spin coating or the like may be used. At least one of thecomplex oxide material and the paraelectric material may be provided ona substrate by using a supercritical fluid.

The complex oxide material having an oxygen octahedral structure is atleast one material selected from a perovskite material, bismuth-layerstructured oxide, superconducting oxide, and tungsten bronze structuredoxide, and the paraelectric material is a layered catalytic compoundwhich includes Si in the constituent elements or a layered catalyticcompound which includes Si and Ge in the constituent elements.

The complex oxide material having an oxygen octahedral structure may beat least one of a perovskite and bismuth layer structured oxide shown byABO₃ or (Bi₂O₂)²⁺(A_(m−1)B_(m)O_(3m+1))²⁻ (wherein A represents at leastone element selected from the group consisting of Li, Na, K, Rb, Pb, Ca,Sr, Ba, Bi, La, and Hf, B represents at least one element selected fromthe group consisting of Ru, Fe, Ti, Zr, Nb, Ta, V, W, and Mo, and m is anatural number of 5 or less), a superconducting oxide shown byLanBa₂Cu₃O₇, Trm₂Ba₂Ca_(n−1)Cu_(n)O_(2n+4), orTrmBa₂Ca_(n−1)Cu_(n)O_(2n+3) (wherein Lan represents at least oneelement selected from the group consisting of Y, La, Ce, Pr, Nd, Pm, Sm,Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu, Trm represents at least oneelement selected from the group consisting of Bi, Tl, and Hg, and m is anatural number from 1 to 5), and a tungsten bronze structured oxideshown by A_(0.5)BO₃ (tetragonal bronze structure) or A_(0.3)BO₃(hexagonal bronze structure) (wherein A represents at least one elementselected from the group consisting of Li, Na, K, Rb, Cs, Pb, Ca, Sr, Ba,Bi, and La, and B represents at least one element selected from thegroup consisting of Ru, Fe, Ti, Zr, Nb, Ta, V, W, and Mo).

The paraelectric material may be a paraelectric material which includesat least one compound selected from the group consisting of CaO, BaO,PbO, ZnO, MgO, B₂O₃, Al₂O₃, Y₂O₃, La₂O₃, Cr₂O₃, Bi₂O₃, Ga₂O₃, ZrO₂,TiO₂, HfO₂, NbO₂, MoO₃, WO₃, and V₂O₅, and SiO₂ or SiO₂ and GeO₂.

The paraelectric material may be a layered compound having an oxygentetrahedral structure which includes at least one compound selected fromthe group consisting of CaSiO₃, BaSiO₃, PbSiO₃, ZnSiO₃, MgSiO₃, B₂SiO₅,Al₂SiO₅, Y₂SiO₅, La₂SiO₅, Cr₂SiO₅, Bi₂SiO₅, Ga₂SiO₅, ZrSiO₄, TiSiO₄,HfSiO₄, NbSiO₄, MoSiO₅, WSiO₅, and V₂SiO₇, or a layered compound havingan oxygen tetrahedral structure which includes at least one compoundselected from the group consisting of CaSiO₃, BaSiO₃, PbSiO₃, ZnSiO₃,MgSiO₃, B₂SiO₅, Al₂SiO₅, Y₂SiO₅, La₂SiO₅, Cr₂SiO₅, Bi₂SiO₅, Ga₂SiO₅,ZrSiO₄, TiSiO₄, HfSiO₄, NbSiO₄, MoSiO₅, WSiO₅, and V₂SiO₇, and at leastone compound selected from the group consisting of CaGeO₃, BaGeO₃,PbGeO₃, ZnGeO₃, MgGeO₃, B₂GeO₅, Al₂GeO₅, Y₂GeO₅, La₂GeO₅, Cr₂GeO₅,Bi₂GeO₅, Ga₂GeO₅, ZrGeO₄, TiGeO₄, HfGeO₄, NbGeO₄, MoGeO₅, WGeO₅, andV₂GeO₇.

An oxide material in which the B site of the perovskite, bismuth-layerstructured oxide, superconducting oxide, or tungsten bronze structuredcompound which makes up the complex oxide material is replaced with Sior Si and Ge may be formed in advance by using a complex polymerizationmethod.

A DLC (diamond-like carbon) film may be formed on a substrate, and thefilm in which the complex oxide material and the paraelectric materialare present in a mixed state may be formed on the DLC film.

A dielectric capacitor according to the present invention comprises alower electrode, a film of the ceramic of the present invention which isformed on the lower electrode, and an upper electrode formed on theceramic film.

In this dielectric capacitor, at least part of the ceramic may have acolumn-shaped structure which is continuous between the upper electrodeand the lower electrode. The diameter of the column-shaped structure maybe 1 to 50 nm.

As examples of the substrate which can be used for the oxideferroelectric material, thin-film fabrication technology, andapplication elements of the present invention, a semiconductor substratesuch as an element semiconductor such as silicon and germanium and acompound semiconductor such as GaAs and ZnSe, a metal substrate such asPt, an insulating substrate such as a sapphire substrate, an MgOsubstrate, SrTiO₃, BaTiO₃, and a glass substrate, and the like can begiven. Of these, a silicon substrate is preferable, and a single crystalsilicon substrate is still more preferable.

An electrode may be formed on the substrate. There are no specificlimitations to the material for the electrode insofar as the material isa conductive material. The electrode may be formed by using a metal suchas Pt, Ir, Au, Al, or Ru, an oxide conductor such as IrO₂ and RuO₂, anitride conductor such as TiN and TaN, or the like. The thickness of theelectrode is about 100 to 200 nm, for example.

Intermediate layers such as an insulating layer and an adhesive layermay be formed between the electrode and the substrate. The insulatinglayer may be formed using SiO₂, Si₃N₄, or the like. There are nospecific limitations to the material for the adhesive layer insofar asthe adhesive layer can secure bonding strength between the substrate andthe electrode or between the insulating layer and the electrode. Forexample, a high-melting-point metal such as tantalum or titanium may beused. These intermediate layers may be formed by using various methodssuch as a thermal oxidation method, CVD method, sputtering method,vacuum deposition method, or MOCVD method.

The ceramic of the present invention may be applied to a dielectriccapacitor, a semiconductor device, and various types of other devices.

FIG. 1 is a cross-sectional view showing a high-dielectric/ferroelectriccapacitor (hereinafter called “ferroelectric capacitor” or“high-dielectric capacitor”) which is manufactured by the manufacturingmethod of the present invention and is used for evaluation of electricalcharacteristics as described later. In this dielectric capacitor, asilicon thermal oxide film 2 is formed on the surface of an n-typesilicon substrate 1 as an interlayer dielectric. A Ti film 3 as anadhesive layer, a Pt lower electrode 4, a ferroelectric film 5 (ceramic)formed of a solid solution of barium strontium titanate which is aperovskite-type ferroelectric material and TiSiO₄ and BaGeO₃ which areparaelectric materials, and a Pt upper electrode 6 are formed on thesilicon thermal oxide film 2 in that order.

FIG. 37 is a cross-sectional view schematically showing a ferroelectricmemory device to which the dielectric capacitor of the present inventionis applied.

A ferroelectric memory device 5000 includes a CMOS region R1 and acapacitor region R2 formed on the CMOS region R1. The CMOS region R1includes a semiconductor substrate 1, an element isolation region 2 anda MOS transistor 3 which are formed on the semiconductor substrate 1,and an interlayer dielectric 4. The capacitor region R2 includes acapacitor C100 consisting of a lower electrode 5, a ferroelectric film6, and an upper electrode 7, an interconnect layer 8 a connected withthe lower electrode 5, an interconnect layer 8 b connected with theupper electrode 7, and an insulating layer 9. The ferroelectric film 6of the capacitor C100 is formed by using the method of manufacturing theceramic of the present invention. An impurity diffusion layer 3 a of theMOS transistor 3 and the lower electrode 5 which makes up the capacitorare connected by a contact layer 11 formed of polysilicon or tungsten.

Examples of a method of manufacturing a multilayer ceramic filmaccording to the embodiment are described below.

Example of manufacture of first multilayer ceramic film

An example of the manufacture of a first multilayer ceramic film isdescribed below. FIG. 39 is a cross-sectional view schematically showingthe manufacturing process for the first multilayer ceramic film.

As shown in FIG. 39A, a main liquid layer 312 for producing aferroelectric is formed on the substrate 10 by using a coating method.As the material for the main liquid layer 312, the first raw materialliquid in the second embodiment and the third raw material liquid in thethird embodiment can be given.

A secondary liquid layer 322 for producing either a ferroelectric or aparaelectric is formed on the main liquid layer 312. As the material forthe secondary liquid layer 322, a material having a crystallizationtemperature lower than that of the material for the main liquid layer312 is selected. In addition, a material which produces an oxide havingno layered structure after crystallization is selected as the materialfor the secondary liquid layer 322. The material for the secondaryliquid layer 322 differs depending upon the material for the main liquidlayer 312. In the case where an SBT-type ferroelectric is formed bycrystallizing the main liquid layer 312, the material for the secondaryliquid layer 322 a is a BiGeO-type material, BiSiO-type material, orSrGeO-type material, for example.

As shown in FIG. 39C, the main liquid layer 312 and the secondary liquidlayer 322 are crystallized by performing a heat treatment, whereby aceramic film 300 consisting of a main crystal layer 310 and a secondarycrystal layer 320 is formed.

According to the example of the manufacture of the first multilayerceramic film, the following effects are obtained.

A material having a crystallization temperature lower than that of themain liquid layer 312 is selected as the material for the secondaryliquid layer 322. Therefore, the secondary liquid layer 322 iscrystallized before the main liquid layer 312 at an initial stage ofcrystallization, as shown in FIG. 39B. As a result, crystals produced inthe secondary liquid layer 322 function as seeds during thecrystallization of the main liquid layer 312. Therefore, crystallizationof the main liquid layer 312 proceeds in the direction from thesecondary liquid layer 322 and from the substrate 10. This enables thegrain size of crystals produced in the main liquid layer 312 to bedecreased.

As the material for the secondary liquid layer 322, a material whichproduces an oxide having no layered structure after crystallization isselected. Therefore, crystals are isotropically grown in the secondaryliquid layer 322. As a result, a secondary crystal layer 320 with a flatsurface is formed, whereby the surface morphology of the ceramic film300 can be improved.

The ceramic film 300 consisting of the main crystal layer 310 andsecondary crystal layers 320 and 330 may be formed by allowing asecondary liquid layer 332 to be interposed between the substrate 10 andthe main liquid layer 312, as shown in FIG. 40A.

Example of manufacture of second multilayer ceramic film

An example of the manufacture of a second multilayer ceramic film isdescribed below. FIG. 41 is a cross-sectional view schematically showingthe manufacturing process for the second multilayer ceramic film.

The example of the manufacture of the second multilayer ceramic filmdiffers from the example of the manufacture of the first multilayerceramic film in that a secondary liquid layer 422 is interposed betweenmain liquid layers 412 and 432.

Specifically, the main liquid layer 412, secondary liquid layer 422,main liquid layer 432, and secondary liquid layer 442 are layered on thesubstrate 10 in that order. A ceramic film 400 consisting of maincrystal layers 410 and 430 and secondary crystal layers 420 and 440 areformed by crystallizing these layers.

As the material for the secondary liquid layers 422 and 442, a materialhaving a crystallization temperature lower than those of the main liquidlayers 412 and 432 is selected in the same manner as in the example ofthe manufacture of the first multilayer ceramic film.

Crystals produced in the secondary liquid layer 422 function as astopper for preventing crystal growth in the main liquid layers 412 and432 by allowing the secondary liquid layer 422 to be interposed betweenthe main liquid layers 412 and 432. Therefore, the grain size ofcrystals in the main crystal layers 410 and 430 formed on opposite sidesof the secondary crystal layer 420 can be decreased.

Example of manufacture of third multilayer ceramic film

An example of the manufacture of a third multilayer ceramic film isdescribed below. FIG. 42 is a cross-sectional view schematically showingthe manufacturing process for the third multilayer ceramic film.

The example of the manufacture of the third multilayer ceramic filmdiffers from the example of the manufacture of the first multilayerceramic film in that a material for a main liquid layer 512 has acrystallization temperature lower than that of the material for asecondary liquid layer 522.

As the material for the main liquid layer 512, the first raw materialliquid in the second embodiment and the third raw material liquid in thethird embodiment can be given. In the case where the material for themain liquid layer 512 produces a PZT-type ferroelectric, the materialfor the secondary liquid layer 522 may be a PbWO-type material or aPbMoO-type material.

A ceramic film having improved surface morphology can be formed bycrystallizing the main liquid layer 512 and the secondary liquid layer522. The reasons therefor are as follows. The material for the mainliquid layer 512 has a crystallization temperature lower than that ofthe material for the secondary liquid layer 522. Therefore,crystallization of the secondary liquid layer 522 proceeds after thecrystallization of the main liquid layer 512, whereby the crystalsproduced from the secondary liquid layer 522 cover a main crystal layer510 produced from the main liquid layer 512. Since the crystals producedfrom the secondary liquid layer 522 do not have a layered structure,crystals produced from the secondary liquid layer 522 are isotropicallygrown. Therefore, a secondary crystal layer 520 with a flat surface isformed. As a result, unevenness of the surface of a ceramic film 500 isdecreased, whereby the surface morphology of the ceramic film 500 can beimproved.

In the examples of the manufacture of the first to third multilayerceramic films, crystal grains produced from the main liquid layer andcrystal grains produced from the secondary liquid layer may be diffusedinto different crystal layers. Moreover, a constituent metal element ofthe main liquid layer may be diffused into the secondary liquid layer,or a constituent metal element of the secondary liquid layer may bediffused into the main liquid layer. Therefore, there may be a casewhere the interface between the main crystal layer produced from themain liquid layer and the secondary crystal layer produced from thesecondary liquid layer is not distinguishable.

Generally, the crystallization temperature has a correlation with themelting point. Specifically, in the case where one of the crystals has acrystallization temperature higher than that of the other crystal, thecrystal having a higher crystallization temperature generally has amelting point higher than that of the other crystal.

Semiconductor Device

A semiconductor device to which a ceramic film obtained by using themethod of manufacturing a ceramic film of the present invention isapplied is described below. This embodiment illustrates a ferroelectricmemory device as an example of the semiconductor device. FIG. 37 is across-sectional view schematically showing a ferroelectric memorydevice.

A ferroelectric memory device 5000 includes a CMOS region R1, and acapacitor region R2 formed on the CMOS region R1. The CMOS region R1includes a semiconductor substrate 1, an element isolation region 2 anda MOS transistor 3 which are formed on the semiconductor substrate 1,and an interlayer dielectric 4. The capacitor region R2 includes acapacitor C100 consisting of a lower electrode 5, a ferroelectric film6, and an upper electrode 7, an interconnect layer 8 a connected withthe lower electrode 5, an interconnect layer 8 b connected with theupper electrode 7, and an insulating layer 9. The ferroelectric film 6in the capacitor C100 is formed by using the method of manufacturing aceramic film of the present invention. An impurity diffusion layer 3 aof the MOS transistor 3 and the lower electrode 5 which makes up thecapacitor are connected by a contact layer 11 formed of polysilicon ortungsten.

In this embodiment, the ferroelectric film 6 of the ferroelectric memorydevice 5000 is formed of the ceramic of the present invention.Therefore, the ferroelectric film 6 has improved surface morphology. Asa result, the thickness of the ferroelectric film 6 can be decreased tosuch an extent that the surface morphology of the ferroelectric film 6is improved. Therefore, according to the ferroelectric memory device5000, a higher degree of integration can be achieved.

A semiconductor device to which the ceramic of the present invention canbe applied is not limited to the ferroelectric memory. The ceramic ofthe present invention may be applied to various types of semiconductordevices such as a DRAM, MIS-type transistor, or MFS-type transistor. Inmore detail, the ceramic of the present invention may be applied to adielectric film of a capacitor for a DRAM or a gate insulating film ofan MIS-type or MFS-type transistor.

The ceramic of the present invention may be applied not only tosemiconductor devices, but also to other applications such as apiezoelectric for piezoelectric devices used for actuators, opticalmodulators, or ultrasonic sensors.

The present invention may have the following features.

First Ceramic Raw Material Liquid

The first ceramic raw material liquid is used by mixing the first rawmaterial liquid and the second raw material liquid. The first ceramicraw material liquid may be a raw material liquid which produces aceramic film by pyrolysis. The first raw material liquid and the secondraw material liquid produce different types of materials. The first rawmaterial liquid and the second raw material liquid may be 1) a liquid inwhich a metal organic compound (metal alkoxide, metal carboxylate, forexample), or a metal inorganic compound (metal nitrate, metal chloride,for example) is dissolved in a solvent (water, alcohol, ester, aliphatichydrocarbon, aromatic hydrocarbon, ketone, ether, mixture of these, forexample), 2) a liquid obtained by subjecting a metal compound tohydrolysis, condensation, and the like in a solvent, or 3) a sol-gelliquid obtained by hydrolysis of a metal alkoxide, for example.

The first raw material liquid and the second raw material liquid aredescribed below in detail.

The first raw material liquid is a raw material liquid for producing aferroelectric having a Bi-type layered perovskite structure. As examplesof a ferroelectric having a Bi-type layered perovskite structure,SrBiTaO-type ferroelectrics (SrBi₂Ta₂O₉, for example), BiLaTiO-typeferroelectrics (Bi_(3.25)La_(0.75)Ti₃O₁₂, for example), and BiTiO-typeferroelectrics (Bi₄Ti₃O₁₂, for example) can be given. The first rawmaterial liquid includes a metal element which makes up a ferroelectric.The amount of the constituent metal element for a ferroelectric includedin the first raw material liquid is determined taking into considerationthe amount of the desired ferroelectric and the ratio of the number ofatoms of the constituent metal elements in the desired ferroelectric.

As specific examples of the first raw material liquid, in the case ofproducing an SrBiTaO-type ferroelectric, a liquid in which solutions ofan alkoxide of strontium, an alkoxide of bismuth, and an alkoxide oftantalum are mixed in 2-methoxyethanol can be given. The concentrationsof the alkoxide of strontium, alkoxide of bismuth, and alkoxide oftantalum in the first raw material liquid may be 0.05 mol/l, 0.1 mol/l,and 1.0 mol/l, respectively. Specifically, the concentrations may be setso that 0.05 mol of an SrBi₂Ta₂O₉ ferroelectric is produced per liter ofthe first raw material liquid.

The second raw material liquid is a raw material liquid for producing anABO-type oxide in which Bi is provided in the A site. If Bi is notprovided in the A site, elements other than Bi may be positioned at thesite of the Bi-type layered perovskite structure at which Bi should bepositioned, whereby the characteristics of the ferroelectric film may beadversely affected. As examples of the ABO-type oxide in which Bi isprovided in the A site, BiGeO-type oxides (Bi₄Ge₃O₁₂, for example),BiMoO-type oxides (Bi₂MoO₆), BiVO-type oxides (Bi₂VO₆), BiCrO-typeoxides (Bi₂CrO₆), BiSiO-type oxides (Bi₄Si₃O₁₂), and BiWO-type oxides(Bi₄W₃O₁₂) can be given. The crystallization temperature of the crystalsproduced from the second raw material liquid can be changed by changingan element in the B site of the ABO-type oxide. The ABO-type oxide maybe either a ferroelectric or a paraelectric. The above oxides may beused individually or in combination of two or more.

The second raw material liquid includes a metal element which makes upthe ABO-type oxide. The amount of the constituent metal element for theABO-type oxide included in the second raw material liquid is determinedtaking into consideration the amount of the desired ABO-type oxide andthe ratio of the number of atoms of the constituent metal elements inthe desired ABO-type oxide.

As specific examples of the second raw material liquid, in the case of aBiGeO-type oxide, a liquid in which solutions of an alkoxide of bismuthand an alkoxide of germanium are mixed in 2-methoxyethanol can be given.The concentrations of the alkoxide of bismuth and alkoxide of germaniumin the second raw material liquid may be 0.20 mol/l and 0.15 mol/l,respectively. Specifically, the concentrations of the alkoxide ofbismuth and alkoxide of germanium may be set so that 0.05 mol of aBi₄Ge₃O₁₂ oxide is produced per liter of the second raw material liquid.

The first raw material liquid and the second raw material liquid arepreferably mixed so that the molar ratio of the ferroelectric producedfrom the first raw material liquid to the ABO-type oxide produced fromthe second raw material liquid is from 100:20 to 100:100.

Example of Manufacture of Ceramic Film

A ceramic film may be formed by using the ceramic raw material liquid ofthis embodiment as follows, for example.

(a) A substrate is subjected to a heat treatment. This heat treatment isperformed to remove moisture present on the surface of the substrate.The heat treatment temperature is 180° C., for example.

b) The ceramic raw material liquid is applied to the substrate, therebyforming a ceramic raw material body layer. As the formation method, spincoating, dipping, and LSMCD can be given.

(c) A solvent in the ceramic raw material body layer is evaporated byperforming a drying heat treatment. The solvent may be evaporated in anitrogen atmosphere. The temperature of drying heat treatment is 160°C., for example.

(d) The ceramic raw material body layer is subjected to a cleaning heattreatment. This heat treatment causes organic substances present in theceramic raw material body layer to be decomposed. The organic substancesmay be decomposed in a nitrogen atmosphere. The heat treatmenttemperature is 260° C., for example.

(e) The ceramic raw material body layer is presintered. Crystal nucleiare formed during presintering. Presintering may be performed in anoxygen atmosphere by RTA, for example.

(f) The ceramic raw material body layer is sintered. Sintering may beperformed in an oxygen atmosphere by FA, for example.

A cycle consisting of the steps (a) to (e) may be repeated two or moretimes.

Effects obtained by depositing a ceramic film by using the ceramic rawmaterial liquid according to this embodiment are described below.

(1) In the case of forming a ferroelectric (SBT) film by sintering theceramic raw material liquid consisting only of the first raw materialliquid, desired characteristics (remanent polarization, for example)required for the ferroelectric film cannot be obtained at a sinteringtemperature of about 700° C.

However, in the case of forming a ceramic film by sintering the firstceramic raw material liquid in a state in which the first raw materialliquid and the second raw material liquid are mixed, desiredcharacteristics required for the ferroelectric film can be obtained evenat a sintering temperature of about 500° C., as described later.According to this embodiment, a ferroelectric film having the desiredcharacteristics can be formed at a lower temperature.

(2) The first raw material liquid and the second raw material liquidproduce different types of materials. Therefore, a crystallizationtemperature at which the first raw material liquid is crystallizeddiffers from a crystallization temperature at which the second rawmaterial liquid is crystallized, for example. As a result, one of theraw material liquids can be crystallized prior to the other raw materialliquid. This enables formation of a ceramic film with improved surfacemorphology.

The above embodiment may have the following features.

(1) A ceramic film may be formed by repeating the above manufacturingsteps for a ceramic film two or more times. A ceramic film may be formedby combining the above manufacturing steps for a ceramic film andmanufacturing steps for a ceramic film using a conventional ceramic rawmaterial.

(2) As the method for forming the raw material body on the substrate byusing the LSMCD method, a method described below can be given. FIG. 38is a cross-sectional view schematically showing an apparatus 200 forforming the raw material body on the substrate by using the LSMCDmethod.

The first raw material liquid 210 is sent to a mesh 240 through anatomizer 230. The first raw material liquid 210 passing through the mesh240 forms a mist 250 and is supplied to the substrate 10. The second rawmaterial liquid 220 is sent to the mesh 240 through an atomizer 232. Thesecond raw material liquid 220 passing through the mesh 240 forms themist 250 and is supplied to the substrate 10. The mist 250 is depositedon the substrate 10, whereby the raw material body is formed. Thediameter of droplets of the mist 250 is 10 to 200 nm, for example.

The first raw material liquid 210 and the second raw material liquid 220may be supplied to the substrate 10 at the same time. Or, the first rawmaterial liquid 210 and the second raw material liquid 220 may besupplied alternately.

In the case of supplying the first raw material liquid 210 and thesecond raw material liquid 220 to the substrate 10 at the same time, theresulting raw material body has a structure in which a first mist 210 aproduced from the first raw material liquid 210 and a second mist 220 aproduced from the second raw material liquid 220 are present in a mixedstate.

The present invention may have the following features.

Second Ceramic Raw Material Liquid

A second ceramic raw material liquid is used by mixing a third rawmaterial liquid and a fourth raw material liquid. The second ceramic rawmaterial liquid may be a raw material liquid which produces a ceramicfilm by pyrolysis. The third raw material liquid and the fourth rawmaterial liquid produce different types of materials. The third rawmaterial liquid and the fourth raw material liquid may be 1) a liquid inwhich a metal organic compound (metal alkoxide, metal carboxylate, forexample) or a metal inorganic compound (metal nitrate, metal chloride,for example) is dissolved in a solvent (water, alcohol, ester, aliphatichydrocarbon, aromatic hydrocarbon, ketone, ether, mixture of these, forexample), 2) a liquid obtained by subjecting a metal compound tohydrolysis, condensation, and the like in a solvent, or 3) a sol-gelliquid obtained by hydrolysis of a metal alkoxide, for example.

The third raw material liquid and the fourth raw material liquid aredescribed below in detail.

The third raw material liquid is a raw material liquid for producing aPZT-type ferroelectric. As examples of PZT-type ferroelectrics,PbZrTiO-type ferroelectrics (PbZr_(y)Ti_(1−y)O₃, for example) andPbLaZrTiO-type ferroelectrics (Pb_(1−x)La_(x)Zr_(y)Ti_(1−y)O₃, forexample) can be given. The third raw material liquid includes metalelements which make up a ferroelectric. The amount of constituent metalelements for a ferroelectric in the third raw material liquid isdetermined taking into consideration the amount of desired ferroelectricand the ratio of the number of atoms of the constituent metal elementsin the desired ferroelectric.

As specific examples of the third raw material liquid, taking aPbZrTiO-type ferroelectric as an example, a liquid in which lead acetatetrihydrate, zirconium butoxide, and titanium isopropoxide are mixed in1-methoxy-2-propanol can be given. The amount of lead acetatetrihydrate, zirconium butoxide, and titanium isopropoxide is determinedtaking into consideration the ratio of the number of atoms of theconstituent metal elements in the desired ferroelectric and the amountof the desired ferroelectric.

The fourth raw material liquid is a raw material liquid for producing anABO-type oxide in which Pb is provided in the A site. If Pb is notprovided in the A site, elements other than Pb may be positioned at thesite of the PZT-type oxide at which Pb should be positioned, whereby thecharacteristics of the ferroelectric film may be adversely affected. Asexamples of the ABO-type oxide in which Pb is provided in the A site,PbGeO-type oxides (Pb₅Ge₃O₁₁), PbMoO-type oxides (Pb₂MoO₅), PbVO-typeoxides (Pb₂VO₅), PbCrO-type oxides (Pb₂CrO₅), PbSiO-type oxides(Pb₅Si₃O₁₁), PbWO-type oxides (Pb₂WO₅), PbSnO-type oxides (PbSnO₃), andPbGeSiO-type oxides (Pb₅Ge₂SiO₁₁) can be given. These oxides may be usedindividually or in combination of two or more. The crystallizationtemperature of the crystals produced from the second raw material liquidcan be changed by changing an element in the B site of the ABO-typeoxide. The ABO-type oxide may be either a ferroelectric or aparaelectric.

As specific examples of the fourth raw material liquid, taking aPbGeO-type oxide as an example, a liquid in which germanium ethoxide andlead butoxide are mixed in 1-methoxy-2-propanol can be given. The amountof germanium ethoxide and lead butoxide is determined taking intoconsideration the ratio of the number of atoms of the constituent metalelements in a desired oxide and the amount of the desired oxide.

The third raw material liquid and the fourth raw material liquid arepreferably mixed so that the molar ratio of the ferroelectric obtainedfrom the third raw material liquid to the ABO-type oxide obtained fromthe fourth raw material liquid is from 100:20 to 100:100.

A ceramic film can be formed by using the second ceramic raw materialliquid in the same manner as in the case of using the first ceramic rawmaterial liquid. In this embodiment, effects the same as those of thefirst ceramic raw material liquid can be obtained.

The present invention is described below by examples.

Example 1

In this example, a Bi₄Ti₃O₁₂ (BIT) film, aBi_(3.3)La_(0.7)Si_(0.7)Ti_(2.25)O₁₂ (BLST) film, and aBi_(3.3)La_(0.7)Si_(0.35)Ge_(0.35)Ti_(2.25)O₁₂ (BLSGT) film formed on aPt electrode were examined. In this example, a pressure post-annealingstep was not performed.

A sol-gel solution for forming a (Bi,La)₄(Si,Ge,Ti)₃O₁₂ ferroelectricwas prepared by mixing a sol-gel solution for forming BIT and sol-gelsolutions for forming La₂SiO₅ and La₂GeO₅. La₂SiO₅ (LSO) and La₂GeO₅(LGO) are layered catalytic oxides.

A sol-gel solution for forming BLST is a solution in which 0.2 mol ofLSO was added to 1 mol of the BIT sol-gel solution. A sol-gel solutionfor forming BLSGT is a solution in which 0.1 mol of LSO and 0.1 mol ofLGO were added to 1 mol of the BIT sol-gel solution.

As a substrate, an Si substrate coated with Pt (Pt/Si substrate) wasused. Thin films with a thickness of 100 nm were formed using thesol-gel solutions for forming a ferroelectric prepared by the aboveprocedure by using spin coating as the deposition method under thefollowing conditions. Crystallization was performed at 550° C., 600° C.,or 650° C. for 20 minutes in oxygen at 1 atm.

Formation conditions for ferroelectric thin film:

(a) Spin coating (500 rpm for 5 sec., 4000 rpm for 20 sec.)

(b) Drying (150° C. for 2 min. in air)

(c) Presintering (400° C. for 5 min. in air)

(d) Sintering (crystallization) (550° C., 600° C., 650° C. for 20 min.by RTA in O₂ at 1 atm)

After sequentially repeating the steps (a), (b), and (c) four times, thestep (d) was performed.

FIG. 2 shows XRD patterns of the ferroelectric thin films obtained inthis example. As shown in FIG. 2, Bi₄Ti₃O₁₂ was crystallized to only asmall extent since a paraelectric pyrochlore phase was present even at650° C. However, BLST and BLSGT were crystallized since the peaks of thecatalytic oxide disappeared. BLST was a randomly orientated filmconsisting of (117) and (001), as shown in FIG. 2. BLSGT was a randomlyorientated film including a large amount of (117) components, as shownin FIG. 50.

A Pt upper electrode was formed on the thin films to obtainferroelectric capacitors. Ferroelectric characteristics of these sampleswere evaluated.

FIG. 3 shows results for the evaluation of D-E hysteresischaracteristics of each sample. BIT did not exhibit ferroelectricitysince the crystallization progressed to only a small extent. BLST andBLSGT showed a hysteresis peculiar to the ferroelectric. As shown inFIG. 3, BLST and BLSGT had a polarization Pr of 13 to 18 μC/cm².However, BLST showed an insufficient hysteresis shape (squareness) incomparison with BLSGT. Therefore, it was confirmed that superiorhysteresis characteristics were obtained by using LSO and LGO as thecatalytic oxides in comparison with the case of using only LSO.

FIG. 43 shows a TEM photograph when completing presintering afterapplying two layers by using the sol-gel solution for forming a BLSGTferroelectric. A great change was observed in the film at this time.Only La₂SiO₅ and La₂GeO₅ were crystallized at this stage. In FIG. 43,the crystallized areas are indicated in white. The crystallized areaswere mainly present at the interface between the layers, in particular,at the interface with the Pt electrode.

FIG. 44 shows results for the measurement of the composition in thelower Pt electrode and the Si substrate (at a depth of 100 μm from theinterface with the SiO₂ thermal oxide film) for BLST and a conventionalBIT thin film when sintering at 650° C. after applying four layers. Inthe case of BLST, elements other than Pt and Si were not detected in thelower Pt electrode and the Si substrate. In the case of conventionalBIT, a large amount of Ti and O (oxygen) were detected in Pt. The sameresults were obtained for BLSGT.

These results suggest that the ferroelectric obtained by the presentinvention was rarely interdiffused into the Pt electrode and the Sisubstrate. This suggests that a large amount of layered catalytic oxidewas present at the interface with the Pt electrode and functioned as adiffusion preventive film.

Example 2

Each capacitor obtained in Example 1 was subjected to pressure annealingat 500° C. for 30 min. at an oxygen partial pressure of 1 atm. or more.XRD patterns and leakage characteristics of these capacitors wereevaluated. FIGS. 4 and 5 show results for the XRD patterns and leakagecurrent density. In the evaluation of the XRD pattern, the pressure ofpressure annealing was set at 1.5 atm., 5 atm., and 9.9 atm. In theevaluation of leakage current density, the pressure was set at 1 atm.(without applying pressure), 3 atm., 6 atm., and 9.9 atm.

As is clear from the XRD patterns shown in FIG. 4, BIT showed a tendencyin which the XRD peak became broad by applying a pressure. The XRD peakof BLST shifted to the higher angle side as the pressure was increased,and the XRD peak intensity was increased. The same tendency as BLST wasconfirmed for BLSGT. Occurrence of a phenomenon in which the XRD peakshifted to the higher angle side and the XRD peak intensity wasincreased suggests that an oxygen deficiency portion in the perovskitelattice was oxidized and compensated for the lattice defect to cause anincrease in bond strength between each atom, whereby the bond distancewas decreased. Specifically, the XRD peak shifts to the higher angleside due to a decrease in the bonding distance, and the XRD peakintensity is increased due to improvement of crystallinity.

As shown in FIG. 5, in the case of performing pressure annealing bysintering at atmospheric pressure, the leakage current density of BLSTand BLSGT was respectively 10⁻⁷ A/cm² and 10⁻⁸ A/cm². In the case ofperforming pressure annealing at 9.9 atm., the ferroelectric capacitorshad a leakage current density of 10⁻⁹ A/cm² and showed almost the sameleakage characteristics. From these results, it was confirmed that theleakage characteristics of BLST are remarkably improved by pressureannealing. In a BIT capacitor formed for comparison, improvement ofleakage characteristics was not observed after applying pressure.

FIGS. 6 and 7 show results for comparison of the surface morphologybefore and after pressure annealing observed using a microscope. Therewas a large difference between BIT and BLST/BLSGT formed by using themethod of the present invention. BLST and BLSGT of the present inventionhad a very dense, flat, and smooth surface morphology.

In the case of BLST, since the crystal grain size was uneven andgenerally small after crystallization at atmospheric pressure as shownin FIG. 7, it is clear that the degree of crystal growth was lower thanthat of BLGST. However, grain growth was promoted by pressure annealing,whereby both BLST and BLSGT were changed into dense, flat, and smooththin films formed of large grains.

From the electron diffraction patterns of BLST before and after pressureannealing, it was found that crystals were almost a single crystal aftergrain growth by pressure annealing (FIG. 8).

The coordination number of Si added to BLST was examined by XPS. Theresults are shown in FIG. 9. A curve indicated by “a” shows the peak ofSi having a coordination number of four in SiO₂. A curve indicated by“b” shows the peak of Si in BLST of this example. Since the 2p peak ofSi in BLST shifted to the high energy side differing from the peak of Sihaving a coordination number of four, it was confirmed that thecoordination number of Si in BLST was six. This suggests that the B siteof the oxygen octahedron in the ferroelectric was replaced with Si. Thesame results were obtained for BLGST. It was found that the B site ofthe oxygen octahedron in the ferroelectric was replaced with Si and Ge.

Reduction resistance of the above BLST capacitor was examined. Thecapacitor was subjected to annealing at 400° C. for 30 min. in nitrogencontaining 3% hydrogen. As a result, almost no change was observed asshown in FIG. 10. It is known that ferroelectric crystals are easilyreduced by hydrogen ions due to strong ionic bonding properties.However, reduction resistance was remarkably improved by allowingelements having strong covalent bonding properties such as Si and Ge tobe introduced into the ferroelectric crystals.

As described above, the crystallization temperature of the ferroelectricthin film of the present invention was decreased by the catalytic effectof a silicate and germanate, which are crystallized at a lowtemperature. Moreover, it was confirmed that the characteristics werefurther improved by using Si together with Ge which has an ionic radiusgreater than that of Si and easily replaces the B site of the oxygenoctahedron in the ferroelectric instead of using only Si.

Example 3

In this example, changes in properties when changing the amount ofBi₂SiO₅ (BSO) from 0.1 mol (R=0.1) to 9 mols (R=9) for 1 mol of aferroelectric material BIT were examined. The film thickness was 100 nmand the crystallization temperature was 600° C. Pressure annealing wasperformed at 500° C. for three hours in oxygen at 9.9 atm. Capacitorswere obtained in the same manner as in Example 1 except for the aboveconditions. XRD patterns and D-E hysteresis characteristics of thecapacitors were evaluated. The results are shown in FIGS. 11 and 12.

As shown in FIG. 11, the peak of BSO was not observed in the XRD patternin the range of 0.1≦R≦1. As shown in FIG. 12, good hysteresischaracteristics were obtained in the evaluation of the D-E hysteresischaracteristics when R=0.1 to 1. The hysteresis shape was improved asthe value for R (molar ratio of catalytic oxide to ferroelectricmaterial) was increased.

As shown in FIG. 11, the peaks of BIT and BSO were observed at the sametime in the XRD pattern when 1<R≦9. It was confirmed that the XRD peakintensity of BSO was increased as the value for R was increased. Asshown in FIG. 13, in the evaluation of the D-E hysteresischaracteristics, the remanent polarization Pr was decreased as the valuefor R was increased to more than 1. However, squareness of thehysteresis characteristics remained good.

Specifically, BSO and BIT form a solid solution in the range of 0.1≦R≦1.In other words, Si in BSO replaces the B site of the oxygen octahedronin BIT. Therefore, the XRD peak of BSO does not exist.

If the value for R exceeds 1, an excess amount of BSO is present in thefilm in comparison with BIT, whereby excess BSO coexists with theBSO-BIT solid solution. Therefore, the XRD peaks of BSO and BSO-BITcoexist. Since the squareness of the resulting hysteresis remains good,BSO-BIT exists as a column-shaped structure interposed between the upperand lower electrodes. In other words, since the density of the BSOcolumns is larger than the density of the BSO-BIT columns as the valuefor R is increased, the ratio of BSO to BSO-BIT is increased. As aresult, the remanent polarization Pr is decreased. This suggests thatthe characteristics of the ferroelectric, in particular, the remanentpolarization can optionally be controlled in the present invention bychanging the value for R.

It is clear that the BSO-BIT solid solution and BSO are in the shape ofa column from cross-sectional TEM photographs shown in FIG. 14. Theaverage diameter of the BSO-BIT columns was 50 nm when R=1. The averagediameter of the BSO-BIT columns was 20 nm when R=5. The average diameterof the BSO-BIT columns was 1 nm when R=9. A D-E hysteresis was notconfirmed when R exceeded 9. Specifically, it is considered that thecolumn-shaped structure could not be formed when R exceeded 9.

Example 4

It is known that a ferroelectric BIT has ferroelectric characteristicsin two directions, and the characteristics are strongly anisotropic. Theferroelectric BIT has a saturation polarization Ps of 50 Mc/cm² in thea-axis direction and 4 Mc/cm² in the c-axis direction. The ferroelectricBIT is a ferroelectric material for which it is necessary to control theorientation corresponding to the purpose of use.

In this example, an amorphous film of DLC (diamond-like carbon) wasformed on a Pt/Si substrate when depositing BIT andBi_(3.3)La_(0.7)Si_(0.35)Ge_(0.35)Ti_(2.25)O₁₂ (BLSGT) of the presentinvention using BIT as a base in order to control the orientation of theupper BLSGT thin film.

A DLC film with a thickness of 20 nm was formed on the Pt/Si substrateat an RF power of 100 W to obtain a substrate 1. A DLC thin film on thesurface of Pt was irradiated with lithium ions from a lithium ion sourceat an angle of 20° in the vertical direction at an RF power of 7.5 kWand an ionization current of 10 pA for 10 seconds to obtain a substrate2. A DLC thin film on the surface of Pt was irradiated with lithium ionsfrom the above lithium ion source in the vertical direction at an RFpower of 7.5 kW and an ionization current of 10 pA for 10 seconds toobtain a substrate 3.

Bi_(3.3)La_(0.7)Si_(0.35)Ge_(0.35)Ti_(2.25)O₁₂ (BLSGT) of the presentinvention was deposited on the above three types of substrates.

A sol-gel solution was synthesized by the following procedure. A sol-gelsolution for forming a (Bi,La)₄(Si,Ge,Ti)₃O₁₂ ferroelectric was preparedby mixing a sol-gel solution for forming BIT and sol-gel solutions forforming La₂SiO₅ (LSO) and La₂GeO₅ (LGO).

A sol-gel solution for forming BLSGT is a solution in which 0.1 mol ofLSO and 0.1 mol of LGO were added to 1 mol of the BIT sol-gel solution.

Thin films with a thickness of 100 nm were formed on the above threetypes of Pt/Si substrates coated with a DLC film by using the sol-gelsolution for forming a ferroelectric prepared by the above procedureunder the following deposition conditions. Crystallization was performedat 550° C. for 20 minutes in oxygen at 1 atm.

Formation conditions for ferroelectric thin film

(a) Spin coating (500 rpm for 5 sec., 4000 rpm for 20 sec.)

(b) Drying (150° C. for 2 min. in air)

(c) Presintering (400° C. for 5 min. in air)

(d) Sintering (crystallization) (550° C. for 20 min. by RTA in O₂ at 1atm.)

After sequentially repeating the steps (a), (b), and (c) four times, thestep (d) was performed.

FIG. 15 shows XRD patterns of three types of ferroelectric thin filmsthus obtained. As shown in FIG. 15, a complete c-axis oriented film wasobtained when using the substrate 1, and a complete a-axis oriented filmwas obtained when using the substrate 2. A complete (117) oriented filmwas obtained when using the substrate 3. These results suggest thatdangling bonds can be formed at an optional density in an optionaldirection by appropriately cutting the carbon-carbon double bonds of DLCby using a certain means. A ceramic thin film oriented in an optionaldirection can be formed by forming a ceramic thin film on DLC. In thisexample, the method for cutting the carbon-carbon double bonds of DLC isnot limited to the lithium ion source insofar as the carbon-carbondouble bonds are appropriately cut.

The method of the present invention is a thin film formation methodusing silicate and germanate catalysts. It is known that one of thefunctions of the catalyst is to reduce the amount of residual carbon.The amount of residual carbon was very small in this example in whichDLC was used as a buffer layer. The effect of this method is maximizedwhen used together with the ferroelectric thin film of the presentinvention.

Example 5

In this example, characteristics of a capacitor in the case of addinglayered catalytic compounds other than La₂SiO₅ and La₂GeO₅ to BIT,SrBi₂Ta₂O₉ (SBT), and PbZr_(0.52)Ti_(0.48)O₃ (PZT) were examined. Asdescribed above, the present invention exhibits a maximum effect byusing a silicate and germanate at the same time. In this example, asilicate and germanate were used at a molar ratio of 1:1. As the layeredcatalytic compound, combinations of MgSiO₃ (MSO)+MgGeO₃ (MGO), Al₂SiO₅(ASO)+Al₂GeO₅ (AGO), La₂SiO₅ (LSO)+La₂GeO₅ (LGO), HfSiO₄ (HSO)+HfGeO₄(HGO), NbSiO₄ (NSO)+NbGeO₄ (NGO), MoSiO₅ (MoSO)+MoGeO₅ (MoGO), WSiO₅(WSO)+V₂GeO₇ (VGO), and V₂SiO₇ (VSO)+V₂GeO₇ (VGO) were used.

The amount of each catalytic compound for 1 mol of each ferroelectricmaterial was as follows. The amount of each catalytic compound was 0.8mol for BIT, 0.66 mol for SBT, and 0.2 mol for PZT. The thickness of thefilm was 70 nm. The crystallization temperature of BIT, SBT, and PZT wasrespectively 600° C., 650° C., and 550° C. Capacitors were formed in thesame manner as in Example 1 except for the above deposition conditions.

The D-E hysteresis characteristics of the resulting samples were good asshown in FIG. 16 (BIT), FIG. 17 (SBT), and FIG. 18 (PZT). Goodferroelectric characteristics were obtained when using the layeredcatalytic compounds of this example. FIG. 16A shows data for the exampleof the present invention, and FIG. 16B shows data for a comparativeexample described later.

In the case of using a Bi-type layered ferroelectric material, it isknown in the art that oxygen deficiency can be compensated for byintroducing multicharged ions such as V or W into the A site of theoxygen octahedron in bulk formation using a solid phase reaction.However, in the case of using spin coating, oxygen deficiency cannot becompensated for, even if W or V is added to the sol-gel solutiondiffering from the case of using the solid phase reaction. This isbecause the material can be crystallized at a temperature as high as1000° C. or more when forming ferroelectric bulk by using the solidphase reaction. However, in the case of forming a thin film by usingspin coating, since lower areas including the lower electrode of theelement are formed in advance, it is necessary to directly form aferroelectric film on the lower electrode. Therefore, the ferroelectricfilm cannot be formed at an excessively high temperature. In this case,the ferroelectric must be formed at 650° C. or less, for example.

As shown in FIG. 16B, good characteristics were not obtained in thecomparative example in which the addition of V was attempted by using asol-gel method. This is considered to be because V was not introducedinto the oxygen octahedral lattice and separated as a low dielectricconstant layer.

As shown in FIG. 16A, in the case of using the layered catalyticcompounds such as V₂SiO₇+V₂GeO₇ (VSO+VGO) of the present invention, goodferroelectric characteristics equal to bulk values were obtained.

Example 6

In this example, among compounds shown by(Bi₂O₂)²⁺(A_(m−1)B_(m)O_(3m+1))²⁻ (wherein A represents at least oneelement selected from the group consisting of Li, Na, K, Rb, Pb, Ca, Sr,Ba, Bi, La, and Hf, B represents at least one element selected from thegroup consisting of Ru, Fe, Ti, Zr, Nb, Ta, V, W, and Mo, and m is anatural number of 5 or less), CaBi₄Ti₄O₁₅ (m=4) was examined. Thethickness of the film was 100 nm, and crystallization was performed at650° C. for 30 min. Other deposition conditions were the same as inExample 1. After forming a Pt upper electrode by vapor deposition,pressure annealing was performed at 500° C. for 30 min. in oxygen at 1.5atm in the same manner as in other examples.

As the raw material sol-gel solution, a solution in which a sol-gelsolution for forming Bi₄Ti₃O₁₂ was added to a sol-gel mixed solution oflayered catalytic compounds CaSiO₃ and CaGeO₃ (molar ratio=1:1) at aratio of 1:1 was used. Specifically, a capacitor having a ferroelectricfilm consisting ofBi₄Ti₃O₁₂+0.5CaSiO₃+0.5CaGeO₃=CaBi₄Ti₃Si_(0.5)Ge_(0.5)O₁₅ was formed.The D-E hysteresis characteristics of this sample were determined. Theresults are shown in FIG. 19. It has not been reported that goodferroelectric characteristics were obtained for this ferroelectricmaterial. However, it was confirmed that good ferroelectriccharacteristics shown in FIG. 19 were obtained by using the presentinvention.

Example 7

In this example, superiority of the present invention was examined forferroelectric materials having a structure other than the perovskitestructure. An Sr₂(Ta_(0.5),Nb_(0.5))₂O₇ (STN) thin film having atungsten bronze structure was formed. This ferroelectric material has asmall remanent polarization and expected to be applied to ferroelectricgate transistors. However, a crystallization temperature as high asabout 950° C. is usually necessary for this ferroelectric material. Thisprevents utilization of this material in practice.

The thin film was deposited under the following conditions. As thesol-gel solutions, a sol-gel solution for forming an SrTaO₃high-dielectric thin film, a sol-gel solution for forming an SrO₂ oxide,and sol-gel solutions for forming NbSiO₄ and NbGeO₄ layered catalyticcompounds were used.

A solution prepared by mixing NbSiO₄ and NbGeO₄ (molar ratio=1:1) with asolution prepared by mixing the sol-gel solution for forming an SrTaO₃high-dielectric thin film and the sol-gel solution for forming an SrO₂oxide (ratio: 1:1) at a ratio of 2:1 to prepare a raw material solutionfor producing Sr₂(Ta_(0.5),Nb_(0.25),Si_(0.125),Ge_(0.125))₂O₇. A thinfilm was formed on a Pt/Ti/SiO₂/Si substrate by spin coating using theabove sol-gel solution. The thickness of the film was 50 nm.Crystallization was performed at 650° C. for 60 min. in an oxygenatmosphere. A Pt upper electrode was then formed. However,ferroelectricity was not confirmed.

Therefore, pressure annealing was performed at 650° C. for three hoursin oxygen at 9.9 atm. as post-annealing. As a result, good crystallinityand good ferroelectric characteristics shown in FIG. 20 were confirmed.It is known that this material has a very high crystallizationtemperature. However, good characteristics were obtained at apractically applicable process temperature by using the mixed catalystof a silicate and a germanate and pressure annealing in an oxygenatmosphere of the present invention.

Example 8

In this example, formation of a thin film from a Bi₂Sr₂Ca₂Cu₃O_(X)(Bi2223) superconducting oxide material was examined instead of aferroelectric. As the layered catalytic compounds, Bi₂SiO₅ (BSO) andBi₂GeO₅ (BGO) were used at a molar ratio of 2:1.

A BSO+BGO mixed sol-gel solution at a molar ratio of 2:1 was mixed witha Bi2223 sol-gel solution to prepare a raw material solution. A thinfilm with a thickness of 50 nm was formed on a Pt/Ti/SiO₂/Si substrateby spin coating using the above sol-gel solution under the followingconditions. Crystallization was performed at 700° C. for 1 min. inoxygen. The film was then subjected to pressure annealing at 700° C. for5 min. in oxygen at 9.9 atm. Crystallinity of the film was confirmed byusing X-ray diffraction. The film had very good surface morphology.

As shown in FIG. 21, the resulting thin film with a thickness of 15 nmwas a good crystal film consisting of a Bi2223 single phase.

As described above, the present invention can be applied to thin filmformation from various types of oxide materials regardless of thecrystal system by utilizing not only ferroelectrics but alsoperovskite-type high dielectrics, Bi-type superconducting materialBi₂Sr₂Ca₂Cu₃O_(X) (Bi2223), or catalytic substances.

Example 9

In this example, formation of a thin film was examined by mixing aBa_(0.5)Sr_(0.5)TiO₃ (BST) perovskite-type high dielectric materialinstead of a ferroelectric and TiSiO₄ and BaGeO₃ paraelectric materialsby using the MOCVD method.

BST has been expected to be a gate oxide film material for the nextgeneration DRAM in place of SiO₂, and studied for ten years or more.However, since a thin film with a thickness of 20 nm or less is rarelyformed from BST while maintaining a high relative dielectric constant,BST has not been put to practical use.

0.25 mol of a BaSiO₃ sol-gel solution and 0.25 mol of TiSiO₄ were mixedwith 1 mol of a BST sol-gel solution to prepare a raw material solution.A thin film with a thickness of 20 nm was formed on a Pt/Ti/SiO₂/Sisubstrate by using the MOCVD method and an MOCVD apparatus shown in FIG.22, using the above sol-gel solution under the following conditions.

The MOCVD apparatus shown in FIG. 22 includes a chamber 20 forperforming MOCVD. The chamber 20 includes a support stage 22 for placinga substrate S10 on which a film is formed, a heater 24 provided in thesupport stage 22, and a nozzle 26 for supplying raw material gas towardthe substrate S10 on the support stage 22. First and second raw materialsupply sections 30 and 34 are connected with the nozzle 26 throughpipes. A gel raw material for forming BST is placed in the first rawmaterial supply section 30. A gel for forming TSO-BGO is placed in thesecond raw material supply section 34. The first raw material supplysection 30 is connected with the nozzle 26 through a pipe 31. The rawmaterial in the first raw material supply section 30 is supplied to thenozzle 26 by carrier gas using helium. The second raw material supplysection 34 is connected with the nozzle 26 through a pipe 35. The rawmaterial in the second raw material supply section 34 is supplied to thenozzle 26 by carrier gas using helium. Oxygen gas is supplied to thenozzle 26 through a pipe 36, and helium gas is supplied to the nozzle 26through a pipe 38. In this example, the MOCVD apparatus includes athermostat 40 in order to prevent a decrease in the temperature of gassupplied to chamber 20 from the nozzle 26. The temperature of the gaswhich is passed through each pipe can be optimized by passing the pipes31, 35, 36, and 38 through the thermostat 40. The pipes 31, 35, 36, and38 may be heated by a heater. A numeral 32 shown in FIG. 22 indicate amass flow controller.

A method of manufacturing a dielectric thin film element examined inthis example is described below.

A silicon thermal oxide film with a thickness of 200 nm was formed bythermally oxidizing the surface of an n-type silicon substrate at 1000°C. A Ti film with a thickness of 30 nm and a Pt film with a thickness of200 nm were formed on the silicon thermal oxide film by sputtering. Thissubstrate was used as a substrate for forming a high-dielectric thinfilm.

A step of forming a mixed thin film of a barium strontium titanateBa_(0.5)Sr_(0.5)TiO₃ (BST) perovskite-type high-dielectric material ofthe present invention and titanium silicate TiSiO₄ (TSO) and bariumgermanate BaGeO₃ (BGO) paraelectric materials (TSO-BGO-BST) on thesubstrate by using the above MOCVD apparatus is described below.

In the MOCVD method, an organometallic raw material containing metalelements of an objective oxide is vaporized by using various methods,and the resulting organometallic vapor is pyrolyzed and crystallizedtogether with oxide gas such as oxygen on the substrate heated and heldin the deposition chamber by using carrier gas such as argon or heliumto obtain the objective oxide thin film. In this example, anorganometallic raw material was prepared by a complex polymerizationmethod. It is important to heat the oxide gas in advance using thethermostat so that heat is not removed from the raw material gas.

The complex polymerization method consists of dissolving a metal nitratein water, forming a metal citrate complex by adding citric acid, forexample, and subjecting the metal citrate complex to esterpolymerization by adding ethylene glycol to obtain a gel. In thisexample, gels for forming BST and TSO-BGO were obtained by this method.

In more detail, water-soluble barium acetate, strontium acetate, andammonium citrate peroxotitanate were used as starting raw materials forforming BST. The above raw materials were dissolved in water. After theaddition of citric acid as an organic additive, the mixture was stirredand heated at about 200° C. to obtain a homogenous gel. If a transparentgel is obtained by this process without causing a precipitate to beformed, it is considered that the metal ions in the raw materials weremicro-mixed. In this example, occurrence of a precipitate was preventedby setting the ratio of the number of moles of citric acid to the totalnumber of moles of metal ions to 5 or more.

A gel for forming TSO-BGO was obtained by the same procedure. As thestarting raw materials, bismuth acetate, ammonium citrateperoxotitanate, silicon acetate, and tetraethyl germanium were used.

After vaporizing the above two types of gels by a bubbling method, thegels were introduced into the chamber together with oxygen gas heatedusing the thermostat in advance by using He carrier gas to form an oxidethin film on the substrate heated at 400° C. The reaction pressure was 5Torr. In order to form a mixed thin film of the present invention, acycle consisting of causing the TSO raw material gas to flow for fiveseconds, causing the BGO raw material gas to flow for five seconds, andcausing the BST raw material gas to flow for five seconds was repeatedten times to obtain a TSO-BGO-BST thin film with a thickness of 20 nm.

A Pt upper electrode (diameter: 100 μmφ, thickness: 100 nm) was formedon the resulting mixed thin film by vapor deposition to form acapacitor. The capacitor was subjected to pressure annealing for threehours in oxygen at 9.9 atm.

FIG. 23 shows an XRD pattern after pressure annealing. Only thecrystallization peak of the paraelectric material appeared beforeapplying pressure. After applying pressure, only the reflection peakfrom BST was detected. This suggests that the constituent elements ofthe paraelectric were taken into the BST crystals.

It was confirmed that the resulting thin film with a thickness of 20 nmwas a very good crystal film from a TEM image shown in FIG. 24.Electrical characteristics relating to a relative dielectric constantand a dielectric loss (tan δ) are shown in FIG. 25. A relativedielectric constant of about 600, which is equal to that of bulk, wasobtained.

Q-E characteristics and leakage current characteristics were shown inFIGS. 26 and 27. The amount of stored charge was about 50 μC/cm² at anapplied voltage of 2 V, and the breakdown voltage was 3 V or more. Theleakage current characteristics of the sample were remarkably improvedafter pressure annealing.

Example 10

A TSO-BGO-BST thin film with a thickness of 20 nm was formed by using athin film formation apparatus using a supercritical fluid. As shown inFIG. 28, an LSMCD apparatus using a supercritical fluid includes a fluidsupplying means 110 which supplies a carbon dioxide (CO₂) fluid in asupercritical state, a deposition raw material container 100 in which adeposition raw material consisting of a polycondensation product ofconstituent elements of an objective metal oxide is placed, an alcoholcontainer 80 in which an alcohol is placed, a mixer 70 which isconnected with the fluid supplying means 110, the deposition rawmaterial container 100, and the alcohol container 80 and forms a rawmaterial fluid by mixing the carbon dioxide, deposition raw material,and alcohol (methanol or ethanol), a nozzle 92, connected with the mixer70, which is disposed in a deposition chamber 90 and sprays the rawmaterial fluid, and a substrate holder 94 which is placed in thedeposition chamber 90 and holds the substrate S10. The mixer 70 is setat a specific temperature by a heating means 120. In FIG. 28, a numeral96 indicates a heater for heating the substrate holder 94, a numeral 98indicates a supersonic oscillator for applying vibration to the nozzle92 or the substrate holder 94, a numeral 97 indicates a pressure gauge,and a numeral 102 indicates a mass flow controller.

In this LSMCD method, a thin film is deposited on the substrate bymixing the polycondensation product and alcohol, mixing the mixture anda fluid or liquid in a supercritical state to form the raw materialfluid, and supplying the raw material fluid to the surface of thesubstrate.

The formation procedure for the TSO-BGO-BST thin film is describedbelow.

As the polycondensation product consisting of the constituent elementsof the metal oxide, the gels for forming BST and TSO-BGO used in theMOCVD method in Example 9 were used. The above two types of gels weremixed in the mixer to prepare a gel for forming TSO-BGO-BST. Afteradjusting the viscosity of the gel by adding ethanol, CO₂ in asupercritical state was added. The mixing molar ratio of the gel forforming TSO-BGO-BST, ethanol, and supercritical CO₂ wasTSO-BGO-BST:ethanol:supercritical CO₂=1:1:1. The coating amount of themixture per application was 50 μl.

The mixed fluid of the gel for forming TSO-BGO-BST, ethanol, andsupercritical CO₂ was applied to the substrate 3 through the nozzle 5disposed in the deposition chamber 1.

After drying (150° C. for two min. in air) and presintering (400° C. forfive min. in air), coating, drying, and presintering were performedagain. The resulting film was then subjected to pressure annealing at450° C. for 30 min. in oxygen at 9.9 atm. A Pt upper electrode(diameter: 100 μmφ, thickness: 100 nm) was formed on the thin film byvapor deposition to obtain a capacitor. The ferroelectriccharacteristics of this capacitor were evaluated. The results are shownin FIG. 29.

This capacitor had good dielectric characteristics with a relativedielectric constant of 500. However, the dielectric characteristics wasa little inferior in comparison with the case of using the MOCVD method.Therefore, the capacitor was subjected to pressure annealing at 450° C.for 30 min. in oxygen at 9.9 atm. As a result, a relative dielectricconstant of 600 was obtained. This is because the interface conditionsbetween the Pt upper electrode and the thin film were improved bypressure post-annealing.

As described above, although pressure annealing had sufficient effectbefore forming the upper electrode, it was particularly effective toperform pressure annealing after forming the electrode, taking intoconsideration the formation of the interface with the electrode.

Example 11

A high-frequency magnetron sputtering apparatus shown in FIG. 30 wasused as a sputtering apparatus. This conventional sputtering apparatusincludes an anode 52 and a cathode 54 facing each other in a chamber 50.A sputtering target 55 is provided on the cathode 54. A support stage 56which supports a substrate S10 on which the film is formed is providedbetween the anode 52 and the cathode 54. A shutter 58 is providedbetween the cathode 54 and the support stage 56.

A sintered body sputtering target used in the present invention wasformed by the following procedure. A 10% Bi-excess SBT target (targetdensity: 50%) was immersed in a mixed solution of a sol-gel solution forforming Bi₂SiO₅ and a sol-gel solution for forming Bi₂GeO₅, and dried at150° C. in air. After repeating this operation five times, the targetwas subjected to heat treatment at 450° C. for 10 min. in air to preparea BSO-BGO-SBT target shown in FIG. 31. A 10% Bi-excess SBT target(target density: 95%) was provided for characteristic comparison.

As a substrate for deposition, a Pt/Ti/SiO₂/Si substrate with dimensionsof 2 cm×2 cm□ was used. After forming BSO-BGO-SBT and SBT thin filmsunder deposition conditions given below, Pt with a diameter of 100 μmφand a thickness of 100 nm was formed by vapor deposition as an upperelectrode to obtain a capacitor sample.

Sputtering Conditions

High frequency output: 200 W

Sputtering gas:Ar:O₂=10:1

Sputtering gas pressure: 15 Pa

Target-substrate distance: 50 mm

Substrate temperature: 650° C.

Sputtering time: 10 min.

FIG. 32 shows an XRD pattern of the resulting BSO-BGO-SBT thin film witha thickness of 100 nm. As shown in FIG. 32, an SrBi₂Ta₂O₉ randomlyoriented film was obtained. The peaks of Bi₂SiO₅ and Bi₂GeO₅ were notincluded as compared to the XRD pattern of the SBT thin film formed forcomparison.

FIG. 33 shows a comparison of TEM images of the cross section of thefilms. There was a large difference in the morphology in cross sectionbetween these films. The BSO-BGO-SBT thin film formed by using theBSO-BGO-SBT target of the present invention was formed of very densecolumn-shaped crystals.

D-E hysteresis characteristics of the sample were evaluated. In the caseof a conventional SBT thin film, a ferroelectric hysteresis was notconfirmed because the leakage current was too large for the filmthickness due to a low density.

In the case of the BSO-BGO-SBT thin film of the present invention, aferroelectric hysteresis shown in FIG. 34 was confirmed although thehysteresis was leaky.

A capacitor having the above BSO-BGO-SBT ceramic film was subjected topressure annealing for three hours in oxygen at 9.9 atm. As a result, aferroelectric hysteresis better than the hysteresis shown in FIG. 34 wasobtained.

Example 12

In this example, a BSO-BIT ceramic thin film of the present inventionwas formed by a solid phase method. A BSO-BIT (molar ratioR=BSO/BIT=0.2/0.8) ceramic was formed by using a conventional solidphase method.

As the starting raw materials, Bi₂O₃, TiO₂, and Si (all powder form)were mixed so that a desired composition (Bi:Ti:Si=1:2.5:0.5) wasobtained. The raw materials weighed using a direct reading balance wereplaced in a polyethylene pot together with an agate stone and acetone.The raw materials were mixed for 10 hours by ball milling. The mixturewas then removed using an enamel vat, dried using a dryer, and formed inthe shape of a column using a mold at a pressure of about 800 kg/cm².The formed product was placed in an alumina crucible and presintered at850° C. for two hours. After presintering, the resulting product wasground by using an alumina mortar to obtain raw material powder forforming a sample.

The raw material powder was formed in the shape of a column togetherwith a small amount of polyvinyl alcohol (binder) by using a mold at apressure of about 800 kg/cm². The binder was removed by maintaining theformed product in an oxidization furnace at 500° C. for two hours. Theformed product was heated at a rate of 200° C./h, maintained at 1100° C.for two hours, and allowed to cool to prepare a column-shaped BSO-BITceramic with a diameter of 10 mm and a thickness of 1 mm. However, sincethe column was collapsed, the ceramic was obtained only in the form ofpowder. The color of the powder was partly black or gray. This suggeststhat the solid phase reaction did not proceed.

In this example, (CH₃)₂Si(OC₂H₅)₂ (liquid) was mixed with Bi₂O₃ so thata desired composition (Bi:Si=2:1) was obtained. The raw materialsweighed using a direct reading balance were placed in a polyethylene pottogether with an agate stone and acetone. The raw materials were mixedfor 10 hours by ball milling. The mixture was then removed using anenamel vat, dried using a dryer, and formed in the shape of a columnusing a mold at a pressure of about 800 kg/cm². The formed product wasplaced in an alumina crucible and presintered at 850° C. for two hours.After presintering, the resulting product was ground by using an aluminamortar to obtain Bi₂SiO₅ (BSO) raw material powder for forming a sample.Bi₂O₃ and TiO₂ were mixed so that a desired composition (Bi:Si=4:3) wasobtained. The raw materials weighed using a direct reading balance wereplaced in a polyethylene pot together with an agate stone and acetone.The raw materials were mixed for 10 hours by ball milling. The mixturewas then removed using an enamel vat, dried using a dryer, and formed inthe shape of a column using a mold at a pressure of about 800 kg/cm².The formed product was placed in an alumina crucible and presintered at850° C. for two hours. After presintering, the resulting product wasground by using an alumina mortar to obtain BIT raw material powder forforming a BIT sample.

The Bi₂SiO₅ raw material powder and BIT raw material powder for forminga sample were mixed together with polyvinyl alcohol (binder), and formedin the shape of a column using a mold at a pressure of about 800 kg/cm².The binder was removed by maintaining the formed product in anoxidization furnace at 500° C. for two hours. The formed product washeated at a rate of 200° C./h, maintained at 950° C. for two hours, andallowed to cool to prepare a column-shaped BSO-BIT ceramic with adiameter of 10 mm and a thickness of 1 mm. As a result, a goodcolumn-shaped BSO-BIT ceramic was obtained. The entire ceramic was denseand black. This suggests that the solid phase reaction was promoted in agood state.

FIG. 35 shows an XRD pattern of this ceramic. In FIG. 35, only randompeaks of BIT were obtained and a peak originating in BSO was notdetected. Therefore, it was confirmed that a good BSO-BIT solid solutionwas obtained in this example. A Pt electrode with a diameter of 1 mmφand a thickness of 300 nm was formed on the upper and lower sides of theresulting column-shaped ceramic to obtain a capacitor sample. Theferroelectric characteristics of this sample were evaluated. As aresult, a good ferroelectric hysteresis shown in FIG. 36 was obtained.

1. A piezoelectric device having a lower electrode, a ferroelectric filmand an upper electrode, the ferroelectric film including: aferroelectric material having a perovskite structure and including atleast bismuth; and a paraelectric material including an oxide thatincludes at least silicon.
 2. The piezoelectric device according toclaim 1, the ferroelectric film further including a paraelectricmaterial including an oxide that includes at least germanium.
 3. Thepiezoelectric device according to claim 2, a molar ratio of germanium tosilicon in the ferroelectric film is 0<Ge/Si≦10.
 4. The piezoelectricdevice according to claim 2, a molar ratio of germanium to silicon inthe ferroelectric film is 0<Ge/Si≦1.
 5. The piezoelectric deviceaccording to claim 1, the ferroelectric film further including aparaelectric material including an oxide that includes at least tin. 6.The piezoelectric device according to claim 5, a molar ratio of tin tosilicon in the ferroelectric film is 0<Sn/Si<9.
 7. The piezoelectricdevice according to claim 1, the ferroelectric film further includinglanthanum.
 8. The piezoelectric device according to claim 1, theferroelectric film further including calcium.